# Previous Colloquium and Videos

### Previous Colloquium and Videos

Date Speaker Title Abstract Video Link
January 10, 2019 Dr. Sergej O. Demokritov - Dept. of Physics, University of Muenster, Germany Room Temperature Bose-Einstein Condensation of Magnons Magnons, which are quanta of high-frequency waves of magnetization, are bosons. At the thermal equilibrium they are described by Bose-Einstein statistics with zero chemical potential, and a temperature dependent density. In the first part of my talk I will demonstrate that by using a technique of microwave pumping it is possible to generate additional magnons in a macroscopic magnetic system based on yttrium iron garnet films and to create a gas of quasi-equilibrium magnons with a non-zero chemical potential. With increasing pumping intensity the chemical potential of the magnons reaches the energy of the lowest magnon state, and a Bose-condensate of magnons is formed [1].
The emerging field of nano-magnonics takes advantage of magnons for the transmission and processing of information on nanoscale. The advent of spin-transfer torque has spurred significant advances in nano-magnonics, by enabling highly efficient local magnon generation in magnonic nano-devices. In the second part of the talk, I will analyze magnons driven by the spin-transfer torque in Py/Pt nano-system from the thermodynamic point of view and will show that they also form a quasi-equilibrium Bose-gas with a non-zero chemical potential, suggesting the possibility of electrically-driven Bose-Einstein condensation of magnons[2].
1. Demokritov et al. Nature, 443, 430 (2006); Demidov et al. PRL, 99, 037205 (2007); Demidov et al. PRL, 101, 257201 (2008); Nowik-Boltyk et al. Sci. Rep. 2, 482 (2012) 2. Demidov et al.  Nat. Mat., 8, 984 (2010); Demidov et al.  Nat. Mat., 11, 1028 (2012); Demidov et al.  Nat. Comm., 8, 1579 (2017)

Video
December 6, 2018 Dr. Mark Vogelsberger - Massachusetts Institute of Technology (MIT) Simulating Galaxy Formation: Illustris, IllustrisTNG and Beyond Cosmological simulations of galaxy formation have evolved significantly over the last years. In my talk I will describe recent efforts to model the large-scale distribution of galaxies with cosmological hydrodynamics simulations. I will focus on the Illustris simulation, and our new simulation campaign, the IllustrisTNG project. After demonstrating the success of these simulations in terms of reproducing an enormous amount of observational data, I will also talk about their limitations and directions for further improvements over the next couple of years. Video
November 29, 2018 Dr. Kalin Vetsigian - University of Wisconsin-Madison Emergent Eco-Evolutionary Phenomena in Microbial Communities The complexity of microbial community dynamics stems not only from the diversity of these communities and the richness of their microbial interactions but also from the fact that many of these interactions can readily evolve. As mutant strains with altered interactions increase in frequency they reshape the ecological dynamics and the selection pressures on existing strains. The spectrum of possible consequences of such an interplay between ecology and evolution are poorly understood. To start filling this gap, we investigated the eco-evolutionary dynamics in communities dominated by toxin-mediated interactions. Such interactions are ubiquitous among soil microbes, and whether and how they contribute to diversity has been a long-standing puzzle. We identified several emergent eco-evolutionary phenomena. First, the dynamics could robustly discover complex evolutionary stable states in which multiple strains coexist (Nash equilibria) despite the fact that such states are unreachable through a step-by-step community assembly. Rather the system as a whole tunnels between collective states via a fundamentally eco-evolutionary process. Second, communities of particular strains can emerge and persist even if these communities are not ecologically stable. Finally, the dynamics can exhibit intermittency in which prolonged periods of apparent community stability are interrupted by periods of fast strain turnover. In spatially structured communities, this intermittency leads to mosaics in which different spatial regions are in different eco-evolutionary regimes in a phenomenon reminiscent of phase coexistence in material science. These findings demonstrate that toxin-mediated interactions are a viable mechanism for explaining diversity, provide a qualitatively new mechanism for adaptive diversification, and expand our understanding of the different possible modes of eco-evolutionary dynamics in microbial communities. Video
November 15, 2018 Dr. Stefano Profumo - UC Santa Cruz What is Dark Matter? Four fifths of the matter in the universe is made of something completely different from the "ordinary matter" we know and love. I will explain why this "dark matter" is an unavoidable ingredient to explain the universe as we observe it, and I will describe what the fundamental, particle nature of the dark matter could possibly be. I will then give an overview of strategies to search for dark matter as a particle, describe a few examples of possible hints of discovery, and outline ways forward in this exciting hunt.
November 8, 2018 Dr. George Becker - UC Riverside, Physics Dept. Connecting Galaxies and the Intergalactic Medium Near Reionization The reionization of hydrogen was a landmark event in cosmic history. Within one billion years of the Big Bang the first galaxies emitted enough ultraviolet photons to ionize the gas in deep space, permanently transforming the Universe. Determining exactly when and how reionization occurred is therefore central to our efforts to understand these early sources, as well as the physics that governs the interaction between galaxies and their environments. I will describe what we know about reionization from the study of quasar absorption lines and other probes of the high-redshift Universe. I will especially focus on what were learning about the intergalactic medium (IGM) shortly after reionization is believed to end. By combining observations of high-redshift quasars with wife-field galaxy surveys we are beginning to better appreciate the complexity of the IGM at this epoch, and recognize how it may help us to construct a more complete model of reionization. Video
November 1, 2018 Stephane Courteau - Queen’s University Puzzles in Galaxy Scaling Relations Galaxies like our Milky Way can be described in terms of their structure, dynamics, and stellar populations. Some very robust correlations between galaxy structural properties, such as total luminosity, maximum circular velocity, and size display rather small scatter, hinting at well-regulated galaxy formation processes. A major challenge to understanding these scaling relations, their tight scatter, and ultimately galaxy formation and evolution, is the elusive interplay between visible and dark matter. I will present the latest results on galaxy scaling relations in order to constrain modern structure formation models as well as the nature and distribution of dark matter in galaxies Video
October 25, 2018 Dr. Mike Pivovaroff - Lawrence Livermore National Laboratory (LLNL) The Quest for Solar Axions: Results from CAST and Prospects for IAXO Determining the nature of Dark Matter (DM) remains one of the most challenging problems in physics. The two leading candidates for DM are weakly-interacting massive particles (WIMPs) and the axion, originally proposed forty years ago as a solution to a problem with the Standard Model of particle physics. In the last decade there has been a renewed interest in axions, as results from the Large Hadron Collider and direct searches have eliminated significant parts of WIMP parameter space. If axions exist, they are continuously produced in our Sun and provide an intriguing avenue for experimental searches using axion helioscopes. In this seminar, I will begin with a brief overview of axion physics and the current experimental landscape. I will then move to a detailed description of the CERN Axion Solar Telescope (CAST), a long-running axion helioscope. I will discuss the key technologies that enable CAST and present recent results which have unprecedented levels of sensitivity over a large range of axion masses. I will conclude with a look towards the International Axion Observatory (IAXO), a next-generation axion helioscope designed to search for axions and axion-like-particle with properties that would not only constitute DM, but possibly address currently unexplained astrophysical observations. Video
October 18, 2018 Dr. Roman Lutchyn - Microsoft Research Topological Quantum Computation with Majorana Zero Modes Research in quantum computing has offered many new physical insights as well as the potential of exponentially increasing the computational power that can be harnessed to solve important problems in science and technology. The largest fundamental barrier to building a scalable quantum computer is errors caused by decoherence. Topological quantum computing overcomes this barrier by exploiting topological materials in which, by their nature, limit errors. In this talk, I will discuss how to engineer topological superconductors at the interface of a conventional superconductor and a semiconductor with spin-orbit interaction. I will review recent experiments aiming to detect Majorana zero-energy modes at the ends of the proximitized nanowires. Finally, I will present designs for scalable quantum computers composed of qubits involving superconducting islands in a Coulomb blockade regime hosting aggregates of four or more Majorana zero modes. Video
October 11, 2018 Gil Refael - Caltech Topological Physics at the Light Matter Interface Topological phases have been appearing everywhere in the past 10 years. They may provide a pathway to protected topological quantum computing, as well as reduced dissipation electronics. Their potential for new quantum devices, however, has been untapped so far. In my talk, I will review the principles behind topological insulators, and then show how these ideas take a new life when applied to systems where light and matter interact. As I will show, the combination of photonics and topology gives rise to topological-polaritons, new paradigms for infra-red detectors and energy harvesting, and new methods for conversion and amplification of law frequency EM radiation. Video
October 4, 2018 Jun Zhu - Penn State University Topological Valleytronics in 2D Materials The advent of two-dimensional materials with hexagonal crystal symmetry offers a new electronic degree of freedom called valley, the manipulation and detection of which could potentially be exploited to form new many-body ground states as well as new paradigms of electronic applications. In this talk, I will describe our effort in creating and understanding valley-momentum locked quantum wires in Bernal stacked bilayer graphene. These quantum wires arise in a topological band structure of bilayer graphene created by state-of-the-art nanolithography and can carry current ballistically with a mean free path of several um’s. They are signatures of the quantum valley Hall effect. I will also demonstrate the operations of a topological valley valve and a tunable electron beam splitter, which exploit unique characteristics of the valley Hall kink states. Remarkably the operation of the valley valve does not require valley polarized current. The high quality and versatile controls of the system open the door to many exciting possibilities in valleytronics and in pursuing fundamental physics of helical 1D systems. Video
October 3, 2018 Nigel Goldenfeld - University of Illinois at Urbana-Champaign Universal Biology, the Genetic Code and the First Billion Years of Life on Earth This colloquium concerns two ideas. First, that there are universal laws of life, which can be deduced by abstracting what we know about life on Earth. Second, universal dynamical signatures of early life, preceding even the last universal common ancestor of all life on Earth, are present in the structure of the modern day canonical genetic code --- the map between DNA sequence and amino acids that form proteins. The code is not random, as often assumed, but instead is now known to have certain error minimisation properties. How could such a code evolve, when it would seem that mutations to the code itself would cause the wrong proteins to be translated, thus killing the organism? Using digital life simulations, I show how a unique and optimal genetic code can emerge over evolutionary time, but only if early life was dominated by collective effects, very different from the present era where individuals and species are well-defined concepts. I will also discuss a second universal signature of life: the complete breaking of chiral symmetry in biological amino acids and sugars, and explain how such transitions can arise in principle as a result of the non-equilibrium dynamics of early-life autocatalytic replicators. Video
September 27, 2018 Dr. Hai-bo Yu - UC Riverside Self-Interacting Dark Matter and Galaxy Rotation Curves Astrophysical observations spanning dwarf galaxies to galaxy clusters indicate that dark matter halos are much more diverse than predicted in the prevailing cold dark matter theory. In this talk, I will show that self-interacting dark matter (SIDM) provides a unified solution to a number of long-standing puzzles in astronomy and astrophysics, including the diverse galaxy rotation curves, the radial acceleration relation and the density cores in galaxy clusters. These results indicate that the inner dark matter halos of the galactic systems are thermalized due to dark matter self-interactions, a significant deviation from the cold dark matter theory. Video
May 31, 2018 Susan Kassin - Space Telescope Science Institute Toward a New Understanding of Disk Galaxy Formation One of the most important open issues in astronomy is the assembly of galactic disks. Over the last decade this has been addressed with large surveys of internal galaxy kinematics spanning the last 10 billion years of the universe. I will discuss recent results from my group that show the kinematic assembly of disk galaxies since a redshift of 2. Our results strongly challenge traditional analytic models of galaxy formation and provide an important benchmark for simulations. Furthermore, I will discuss our plans for using the multi-object spectrograph on JWST to enrich our understanding of galaxy kinematics at intermediate redshifts, and to extend our measurements to potentially unvirialized systems in the much earlier universe. From mock JWST observations of zoom-in simulations of galaxies, we are finding that interpreting these observations is not necessarily straightforward.
May 24, 2018 Vid Irsic - University of Washington Small Scale Structure of the IGM: A Dark Matter Tale The intergalactic medium (IGM) plays a unique role in constraining the (small scale) matter power spectrum, since the low-density, high redshift IGM filaments are particularly sensitive to the small-scale properties of dark matter. The main observable manifestation of the IGM, the Lyman-alpha forest, has provided important constraints on the linear matter power spectrum, especially when combined with cosmic microwave background data. This includes, most notably, the tightest constraints on warm dark matter (WDM) and fuzzy dark matter (FDM) models, that I will present in this talk.
May 17, 2018 Smadar Naoz - University of California, Los Angeles (UCLA) Triples are Here and There, Triples are Everywhere
(Triples in Planets, Stars, and Balck holes)
Many observed triple systems in our Universe are in a hierarchical configuration: two objects orbit each other in a relatively tight inner binary while the third object is on a much wider orbit. In this case, the secular approximation (i.e., phase-averaged, long-term evolution) can be applied, where the interactions between two non-resonant orbits are equivalent to treating the two orbits as massive wires. Thus, the orbits may change shape and orientation, on timescales longer than the orbital periods, but the semi-major axes are constant. This approximation has been proven to be very useful in many astrophysical contexts, from planetary to triple-star systems and even black holes. I will discuss recent developments in that field and will show that hierarchical triple systems are richer and far more exciting than considered of before. In particular, the tight orbit can reach extremely high eccentricities and undergo chaotic flips of its orientation. This behavior has important implications for the evolution of many systems, and I will present some seminal examples, such as retrograde hot Jupiters, blue stragglers, and black-hole binaries.
May 10, 2018 Andrew Fruchter - Space Telescope Science Institute (STScI) Refusing to Go Quietly: Gamma-Ray Bursts, Superluminous Supernovae and their Progenitors Gamma-ray bursts (GRBs) are the most brilliant objects in the universe. Some are initially bright enough to be seen by the unaided eye to a redshift of one. Yet the majority of GRBs, the so-called long-soft GRBs (LGRBs) are, like most supernovae, produced by the collapse of a massive star. I will discuss the environmental conditions and stellar progenitors which in rare circumstances create these unusually brilliant explosions and with them the most relativistic bulk motion known. I will show that properties of an unusual GRB, GRB 111209a, and strong similarities between the hosts hydrogen-poor Superluminous Supernovae (SLSNe) and LGRB hosts suggest that LGRBs and SLSNe may have been particularly prevalent the early universe, and that the similar local environments in which they are found may be an important component in the formation of the central engines that power these events. I will also use measurements of the relativistic outflow of LGRBs to place some limits on the central engines. Short Bio: Andy Fruchter received his PhD working with Joe Taylor at Princeton on millisecond pulsars, then went on to a Teagle Fellowship at the Department of Terrestrial Magnetism of the Carnegie Institution and a Hubble Fellowship at Berkeley. After Berkeley he joined the staff of the Space Telescope Science Institute (STScI) where, working with Richard Hook, he developed the Drizzle algorithm for handling the image processing of the Hubble Deep Field, which became the primary algorithm for combining Hubble Space Telescope (HST) images. At STScI he continued his work on compact objects and their progenitors. He was a member of the Supernova Cosmology Project which was one of the two teams responsible for discovering the acceleration of the expansion of the universe. He has also lead a number of large programs studying gamma-ray bursts and their host environments, and has most recently been involved in HST observations of the merging neutron star binary, GW 170817.
May 3, 2018 Adrian Liu - UC Berkeley & McGill University 21cm Cosmology in the Detection Era Although it is a crucial part of our cosmic timeline, Cosmic Dawn—when the first stars and galaxies formed and systematically reionized the intergalactic medium—remains relatively unexplored. By tracing the distribution and state of neutral hydrogen, 21cm cosmology promises to provide the first direct observations of Cosmic Dawn. The Hydrogen Epoch of Reionization Array (HERA) is a low-frequency radio interferometer that is poised to realize this promise within the next few years by making large-scale observations of the 6 < z < 20 universe. In this talk, I will provide an overview of the scientific capabilities of HERA as well as a status update on high-z 21cm cosmology. As part of this update, I will discuss a recently claimed first detection of the 21cm line at z~17 from the Experiment to Detect the Global EoR Signal (EDGES). If confirmed, the EDGES result would have broad-ranging implications not just on the astrophysics of the first stars, but possibly also the physics of dark matter.
April 19, 2018 Miguel Mostafa - Pennsylvania State University Multi-Te V Particle Astrophysics with the HAWC Observatory High-energy gamma-ray observations are an essential probe of cosmic-ray acceleration mechanisms. The detection of the highest energy gamma rays and the shortest timescales of variability are the key to improve our understanding of the acceleration processes and the environment of the cosmic accelerators. The High Altitude Water Cherenkov (HAWC) experiment is a large field of view, multi-Te V, gamma-ray observatory continuously operating at 14,000 ft since March, 2015. The HAWC observatory has an order of magnitude better sensitivity, angular resolution, and background rejection than the previous generation of water-Cherenkov arrays. The improved performance allows us to discover Te V sources, to detect transient events, to study the Galactic diffuse emission at Te V energies, and to measure or constrain the Te V spectra of Ge V gamma-ray sources. In addition, HAWC is the only ground-based instrument capable of detecting prompt emission from gamma-ray bursts above 100 Ge V. In this colloquium I will present the most recent results using the first three years of data from the HAWC observatory. I will also briefly mention the exciting perspectives of building a next-generation gamma-ray experiment at a very high altitude in the Southern Hemisphere. Short Bio: Miguel Mostafa is a professor of physics and of astronomy & astrophysics at Penn State University. After obtaining his Ph.D. in high energy particle physics from Instituto Balseiro in Argentina, he was a fellow of the Instituto Nazionale di Fisica Nucleare in Italy, and a postdoctoral research associate at the University of New Mexico. He was an assistant professor of physics at the University of Utah, and an associate professor of physics at Colorado State University before joining Penn State in 2013. He has been working on ultra-high energy cosmic rays as a member of the Pierre Auger Collaboration, and he is the PI of the Astrophysical Multi-Messenger Observatory Network at Penn State since 2013. His research interests are in high energy particle astrophysics, including the origin of cosmic rays, acceleration mechanisms, particle physics at energies above terrestrial accelerators, gamma-ray astronomy and the structure of the Galaxy, and the nature and properties of dark matter. He was elected fellow of the American Physical Society in 2016, and his teaching awards include the C.I. Noll Award for Excellence in Teaching at Penn State, Best Teacher Awards and the Outstanding Mentor Award at Colorado State University, and the Students Choice Award at the University of Utah.
April 12, 2018 David Reitze - California Institute of Technology The Gravitational Wave Astronomical Revolution We are witnessing a revolution in astrophysics brought about by the first direct detections of gravitational waves by LIGO and Virgo. Twenty years ago many wondered when or even if gravitational waves could be detected on earth; today observations of binary black hole mergers detected through their gravitational wave emissions are becoming routine. The first observation of two colliding neutron stars in August 2017, captured both in gravitational waves and in light, has given us new insights into gamma ray bursts, kilonovae, the formation of heavy elements, and even gravity itself. Gravitational waves provide unique information about the most energetic astrophysical events, revealing insights into the nature of gravity, matter, space, and time. In this talk, I’ll cover gravitational waves and what makes them so difficult to detect and at the same time such powerful and unique probes of the universe. Most of the presentation will focus on the interferometers, the LIGO-Virgo detections and their astrophysical implications. Time permitting, I’ll give a preview of where LIGO intends to go in the next decade and beyond.
April 5, 2018 Yuval Grossman - Cornell University Neutrinos as the Key to the Universe as We Know It Why is there only matter around us? How neutrinos acquire their tiny masses? Why all particles in Nature have integer electric charges? It turns out that these open questions maybe related. In this talk I will explain these open questions, the connection between them, and describe the on-going theoretical and experimental efforts in understanding them.
March 15, 2018 Alexander Grosberg - New York University Activity Driven Segregation of Phases in Particles and (Bio)Polymers Big nuts segregate from small ones; oil segregates from water; but there is also another novel type of segregation, activity driven, which may be important for the functioning of our chromosomes. Video
March 8, 2018 Rafael Lang - Purdue University Xenon and the Hunt for Dark Matter The Nature of Dark Matter is one of the biggest outstanding problems in physics. I will review the evidence for Dark Matter from cosmological and astrophysical arguments, spanning vast time and length scales. Some leading candidate models will be introduced. In particular, the search for WIMP particles is led by Xenon-based detectors. With target masses exceeding a tonne, these detectors are now also sensitive to signals from solar and supernova neutrinos. With their extraordinary sensitivity even to single electrons, new experiments to search for sub-GeV dark matter become possible. I will report on results and the status of the XENON1T experiment as well as its upgrade XENONnT, will introduce the LBECA experiment to search for sub-GeV dark matter, and will give an outlook both for the search for dark matter as well as for neutrinoless double-beta decay. Video
March 1, 2018 Benjamin Lev - Stanford Exploring quantum thermalization with a magnetic quantum Newton’s cradle The question of how chaos arises in nature touches on widely disparate phenomena. For example, the fact that chaos emerges gradually in weakly nonlinear systems unpins our explanation for why the solar system remains stable. While the work of Kolmogorov and others in the 1950’s provided a firm connection between the theories of classical mechanics and classical statistical mechanics by showing how classical chaos and thermalization emerge, the analogous question in quantum physics remains a key unresolved question. How, specifically, does quantum chaos—and hence, thermalization—emerge in isolated quantum systems? We will present a new experiment that explores this question by studying the dynamics of the momentum in a dipolar quantum Newton's cradle consisting of highly magnetic dysprosium atoms. This system constitutes the first dipolar strongly interacting 1D Bose gas. The dipolar interactions provide tunability of both the strength of the integrability-breaking perturbation and the nature of the near-integrable dynamics. The work sheds light on the mechanisms by which isolated quantum many-body systems thermalize and on the temporal structure of the onset of thermalization.
February 22, 2018 Nitya Kallivayalil - University of Virginia Probing the Dark Halo of the Milky Way The Local Group, the regime in which detailed star-by-star studies can be done, is becoming a major testbed for the cold dark matter-based model of the Universe. Critical to these tests is a better estimate of the total Milky Way halo mass. The most reliable means by which to constrain the properties of the Milky Way dark halo is through assessing the 6-D phase space distributions of tracers of its gravitational potential. This requires accurate proper motions (tangential velocities) in addition to generally known radial velocities for field stars, streams, and satellite galaxies widely distributed throughout the halo. In turn, these measurements allow us to investigate the past histories of these tracers, and thus the accretion history of the Milky Way. I will discuss some novel approaches we have been developing to obtain proper motions for a variety of tracers in the Milky Way halo, including streams, globular clusters, and satellite galaxies, to definitively constrain the Milky Way's dark halo mass, shape and distribution. These techniques involve space-based imagers (HST), wide-field ground-based imagers, as well as imagers equipped with adaptive optics systems. I will also discuss the future prospects for this work, and the trade-off between Gaia, space missions (JWST, WFIRST, EUCLID), and ELTs. Video
February 15, 2018 Abhay Deshpande - Stony Brook University The Science and Status of the U.S. Electron Ion Collider Quantum Chromodynamics (QCD) is no doubt the correct theory of strong interaction within the Standard Model of Physics. However, despite decades of significant theoretical progress made based on a broad range of experimental observations, some of the most intellectually compelling questions remain unanswered. For example, how do quark, gluons and their interactions & dynamics, collectively result in the observed fundamental properties of hadrons such as the spin and mass? What is the QCD/partonic origin of the nucleon-nucleon forces in nuclei? How does nuclear environment impact the parton’s momentum distribution in confined nucleons? Does the gluon density in nucleons and nuclei saturate at extremely high energy, and form a universal form of gluonic matter? What connections can be made between the understanding of cold QCD matter in a nucleus to the hot Quark Gluon Plasma that emerges when two nuclei collide at the LHC and RHIC? Such questions can now be addressed qualitatively through a polarized high-energy high-luminsity Electron Ion Collider (EIC). Along with the advances in accelerator technology, lessons from the limitations experience in past fixed target and collider experiments will impact the future detector and interaction region designs for this future collider. Last, but certainly not the least, the theoretical frame work is mature enough to put the resulting measurements in to comprehensive picture within QCD that could answer the above compelling questions. The Electron ion collider (EIC) was recommended in the 2015 US Longe Range Plan prepared by the US Nuclear Science Advisory Committee (NSAC) as the highest priority for new construction for a new facility within the US. In this talk, I will summarize its science case, and present the status and plans for its realization. Video
February 8, 2018 Sayantani Ghosh - UC Merced Directed nano-assembly of adaptive functional structures The design and development of adaptive functional structures using artificially synthesized nano-constituents as building blocks is one of the most compelling current research areas. The typical approach is bottom-up assembly of nanoparticles (NPs), and while this has led to the successful creation of two- and three-dimensional super-lattices, these tend to simply exhibit the combined properties of the constituent NPs, instead of exhibiting a novel functionality arising from synergistic inter-particle interactions. The route we use involves utilizing soft materials such as liquid crystals as templates for NP assembly, which removes rigid constraints in the way the individual components can be combined and make novel architectures possible, such as non-planar structures. Additionally, it allows us to modulate the NP assembly in situ via external controls, such as temperature, mechanical strain and electromagnetic fields, which lead not just to greater versatility in functionality, but to the emergence of entirely novel behavior. Following this approach, we demonstrate “cluster assembly” of metallic, magnetic and semiconducting NPs that form structures with interesting new properties and diverse applications in magneto-optical sensing, photothermal therapy, and tissue engineering. This work was funded by NSF and UCMEXUS-CONACYT. Video
February 1, 2018 Chetan Nayak - UCSB Thermalization and its Discontents Thermalization is the process by which a typical closed quantum system in a generic initial state approaches local thermal equilibrium. Its occurrence precludes some fascinating and potentially useful equilibrium states of matter. However, under certain conditions, thermalization only occurs after an exponentially long time. During the intervening time interval, which is called the prethermal regime, most of the beneficial properties associated with thermal equilibrium continue to hold, but some of the limitations are removed. As a result, states of matter such as time crystals and self-correcting quantum memories can occur. Video
January 25, 2018 Joshua Lui - UCR Observation of Valley-Exclusive Bloch-Siegert Shift in Monolayer WS2 Coherent interaction with off-resonance light can be used to shift the energy levels of atoms, molecules, and solids. The dominant effect is the optical Stark shift, but there is an additional contribution from the so-called Bloch-Siegert shift that has eluded direct and exclusive observation in solids. We observed an exceptionally large Bloch-Siegert shift in monolayer tungsten disulfide (WS2) under infrared optical driving. By controlling the light helicity, we could confine the Bloch-Siegert shift to occur only at one valley, and the optical Stark shift at the other valley, because the two effects obey opposite selection rules at different valleys. Such a large and valley-exclusive Bloch-Siegert shift allows for enhanced control over the valleytronic properties of two-dimensional materials. Reference: Large, valley-exclusive Bloch-Siegert shift in monolayer WS2. E. J. Sie, C. H. Lui, Y.-H. Lee, L. Fu, J. Kong & N. Gedik Science 355, 1066-1069 (2017) Biography: Prof. Chun Hung (Joshua) Lui joined the Department of Physics at UC Riverside as an assistant professor in July 2015. Before that he was a postdoc at MIT. He obtained his Ph.D. in physics at Columbia University in 2011. His group investigates the light-matter interactions in 2D layered materials, such as graphene and transition-metal dichalcogenides, by means of Raman, infrared, and ultrafast pump-probe laser spectroscopy and imaging. Video
January 18, 2018 Jim Thomas - Lawrence Berkeley National Laboratory The Chiral Magnetic Effect in Hot QCD I will give a brief introduction to the world of Hot QCD at the Relativistic Heavy Ion Collider and the unusual opportunities that it provides for the experimentalist. Heavy Ion Collisions allow us to study nuclear matter at high temperature (150 MeV) and high density (10x normal nuclear matter densities). These are conditions that are similar to the conditions in the early Universe a few microseconds after the Big Bang. Heavy ion collision also provide systems with high angular momentum (1000 h-bar), and they create extremely large magnetic fields (10^17 gauss). One application of these high magnetic fields is the Chiral Magnetic Effect. If the CME can be found experimentally, it would be the smoking gun for Chiral symmetry restoration in heavy ion collisions, as well as the observation of parity violation in the strong interaction (in hot QCD). I will discuss the phenomenology of the CME and give an update on the status of the experimental search for it.
January 11, 2018 Yun-Tse Tsai - SLAC Exploring Neutrino Territory: Using LArTPC Technology Neutrinos are the electrically neutral elementary particles with finite mass. The discovery of the non-zero masses is the first instance of a conflict with the Standard Model of particle physics, which has successfully described elementary particles and interactions but leaves questions unanswered. The fruitful results from neutrino experiments in the past two decades have opened a window to a new territory, and further measurements are required to address fundamental questions. In this talk, I will introduce the core topics of neutrino physics, the requirements of neutrino experiments, focusing on the technology of liquid argon time projection chamber (LArTPC). In particular, I will discuss measuring neutrinos from supernova explosions and searching for exotic physics with LArTPCs. I will talk about the MicroBooNE experiment, the first large LArTPC in the U.S., its recent results, and the future LArTPC experiments.
December 7, 2017 Jay Wacker Physicists at Startups I recently left an academic physics career to join a tech startup called Quora Quora is questions and answer knowledgebase whose mission is to share and grow the world's knowledge. I'll discuss why I made this career change, why physicists can make a great impact at startups, and my observations from my time outside of physics. Video
November 30, 2017 Wilson Ho STM Inelastic Electron Tunneling Spectroscopy and Microscopy Inelastic electron tunneling in a scanning tunneling microscope (STM) provides a unique way to measure and image the excitation of an atom or molecule adsorbed on a solid surface with sub-Ångstróm resolution. Inelastic electron tunneling spectroscopy (IETS) and microscopy was first reported in 1998 for the detection of vibrational excitation in a single molecule and has since been extended to the excitation of a single electron spin and the rotation of a single molecule. This talk illustrates by three examples the use of STM-IETS to image the nature of the chemical bond in molecular structure and intermolecular interactions, spin-vibration coupling in single molecule magnetism, and single molecule vibration and dynamics in the time domain. Video
November 16, 2017 Andrea Young Topological order and symmetry breaking in van der Waals heterostructures

Correlated quantum states of matter can be distinguished by their symmetry, their topology, or both.  Examples of symmetry-breaking in solid state systems abound, and include most familiar phases of matter, such as ferromagnetism, superconductivity, and crystalline order.  Topological order is much rarer experimentally, having only been definitively observed at partial filling of Landau levels—flat bands of electronic states that develop when two-dimensional electrons are subjected to a large magnetic field.  Topological order manifests through global properties of the many-body wavefunction, encoded in the fractionally quantized Hall effect and fractional quantum numbers of the collective excitations supported by the interacting electron system. Theoretically, topological order can also arise within generalized ‘Chern bands,’ of which Landau levels are a limiting case.  Most famously, electrons subjected simultaneously to a periodic potential and magnetic field are confined to the fractal bands of the Hofstadter butterfly, each of which is a Chern band.

In this talk, I will describe the experimental observation of ‘fractional Chern insulators’ in van der Waals heterostructures created by combining atomically thin graphite and insulating hexagonal boron nitride.  van der Waals heterostructures provide an ideal experimental platform for investigating the correlated physics of Chern bands, allowing superlattice potentials (engineered from the interference of the mismatched graphene and boron nitride lattices) to be combined with exceptionally low disorder and strong interactions. I will describe how we distinguish the fractional Chern insulators—which feature fractionally charged excitations--from the other gapped electronic phases in these devices including those that break lattice symmetries.  Finally, I will describe prospects for using fractional Chern insulators as a substrate for engineering and detecting novel emergent quasiparticles with unconventional quantum statistics.

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November 9, 2017 Alex Travesset Nanoparticle Assemblies as a New Form of Matter Materials whose fundamental units are nanoparticles, instead of atoms or molecules, are a new form of matter that is gradually emerging as major candidates to solve many of the technological challenges of our century. Those materials display unique structural, dynamical and thermodynamical properties, often reflecting deep underlying geometric and topological constraints. In this colloquia, I will discuss the assembly of these materials into crystals or quasi-crystals, so-called nanoparticle superlattices. I will introduce three successful strategies to induce crystallization into simple and binary lattices: DNA programmable self-assembly, crystallization of nanoparticle neutral (uncharged) polymer brushes by electrostatic phase separation and also, by controlling self-assembly through hydrocarbon and polystyrene capping ligands. I will show that the structure of superlattices follows from considering capping ligands as Skyrmions with vortex textures, which determine the bonding very much like atomic orbitals in lattices of simple atoms. I will also discuss the underlying icosahedral order present in all experimental superlattices reported so far, and discuss a wealth of experimental data and numerical simulations providing confirmation of the theoretical predictions. I will finish with an outlook for this fascinating new materials.
November 2, 2017 Nathaniel Gabor Why Are Terrestrial Plants Green? And Other Essential Questions About Emerging Quantum Optoelectronic Technologies Nature realizes a vast array of complex structures composed of molecular building blocks, the electronic structure of which can be well described by quantum mechanics. In photosynthetic light harvesting, for example, quantum behavior within complex nanoscale structures has generated tremendous recent interest. While there is remarkable potential that photosynthetic systems are, in a sense, behaving as quantum devices, the exact relationship between structure and the properties of quantum states (e.g., coherence) remains a topic of vigorous debate. In this talk, I describe a new paradigm – based on internal thermodynamic fluctuations in a QHE photocell – that attempts to describe highly efficient light energy harvesting in complex quantum structures. By understanding the connection between electronic structure and energy fluctuations, I describe an intrinsic regulation mechanism that emerges from quantum structure alone. Beyond gaining a deeper understanding of quantum optoelectronics, the natural regulation process described here promises to have applications across various disciplines ranging from quantum nanoscience and computing to bionanoscience and astrobiology. Natural regulation may also explain the predominance of green plants on Earth. Video
October 26, 2017 Yaroslav Tserkovnyak Spin hydrodynamics in insulators I will review recent progress in understanding novel transport phenomena in magnetic insulators. Central to this will be conservation laws that are rooted in topological invariance of certain types of magnetic field configurations. The continuity relations associated with such dynamic spin textures can mimic superfluid phenomena, even at high temperatures. Key examples will include easy-plane magnetic films, materials that harbor skyrmionic textures, and, surprisingly, disordered glassy spin systems. Recently developed magnetoelectric and thermoelectric techniques (e.g., based on spin Hall and spin Seebeck effects) are now allowing us to systematically access this physics in a range of materials, both old and new. Video
October 19, 2017 Carl Wieman Taking a scientific approach to teaching physics (and most other subjects)

Guided by experimental tests of theory and practice, science has advanced rapidly in the past 500 years.  Guided primarily by tradition and dogma, science education meanwhile has remained largely medieval.  Research on how people learn is now revealing much more effective ways to teach and evaluate complex thinking and learning than what is in use in the traditional science class.  Students and instructors find such innovative research-based teaching more rewarding, because they involve the physics expertise of the instructor much more extensively and transfer that expertise more effectively. This research is setting the stage for a new approach to teaching and learning that can provide the relevant and effective science education for all students that is needed for the 21st century.  I will also cover more meaningful and effective ways to measure the quality of teaching. Although the focus of the talk is on undergraduate science and engineering teaching, particularly physics, the underlying principles come from studies of the general development of expertise and apply widely.

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October 12, 2017 Hilke E. Schlichting Planet Formation at Home and Abroad Recent observations by the Kepler space telescope have led to the discovery of more than 4000 exoplanet candidates consisting of many systems with Earth- to Neptune-sized objects that reside well inside the orbit of Mercury, around their respective host stars. How and where these close-in planets formed is one of the major unanswered questions in planet formation. I will present new results that self-consistently treat the nebular gas accretion onto rocky cores and the subsequent evolution of gas envelopes due to cooling and photo-evaporation following the dispersal of the protoplanetary disk. I will demonstrate that planets shed their outer layers (dozens of percent in mass) following the disk's dispersal (even without photo-evaporation), and that their atmospheres shrink in a few Myr to a thickness comparable to the radius of the underlying rocky core. In addition, I will discuss the importance of collisions in shaping the architecture and composition of super-Earths. Finally, I will conclude with comparing our new results with observations and discussing the implications for the origin and formation of terrestrial planets in our solar system and for close in exoplanets. Video
October 5, 2017 David Simmons-Duffin The conformal bootstrap: magnets, boiling water, and quantum gravity

Conformal Field Theory (CFT) describes the long-distance dynamics of quantum and/or statistical many-body systems. Often, this dynamics is so complicated that traditional computational tools fail.

However, powerful new techniques for understanding CFTs have emerged in the last decade, based on the old idea of the "conformal bootstrap". I will describe how the bootstrap lets us calculate critical exponents in the 3d Ising Model to world-record precision, how it explains striking relations between magnets and boiling water, and how it can be applied to questions across theoretical physics.

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September 28, 2017 Jianwei (John) Miao Exploring the #D Nano and Atomic World: Coherent Diffractive Imaging and Atomic Electron Tomogrpahy Crystallography has been fundamental to the development of many fields of science over the past century It has now matured to a point that as long as good quality crystals are available, their atomic structure can be routinely determined in three dimensions. However, many samples in nature are non-crystalline and their three-dimensional (3D) structures are not accessible by crystallography. Overcoming this hurdle has required the development of new structure determination methods. In this talk, I will present two methods that can go beyond crystallography: coherent diffractive imaging (CDI) and atomic electron tomography (AET). In CDI, the diffraction pattern of a non-crystalline sample or a nanocrystal is first measured and then directly phased to obtain an image. The well-known phase problem is solved by combining the oversampling method with iterative algorithms. In the first part of the talk, I will illustrate several important CDI methods and highlight some important applications in the physical and biological sciences using 3rd generation synchrotron radiation and X-ray free electron lasers. In the second part of the talk, I will present a general tomographic method, termed AET, for 3D structure determination of crystal defects and disordered materials at the individual atomic level. By combining advanced electron microscopes with novel data analysis and tomographic reconstruction algorithms, AET has been used to reveal the 3D atomic structure of crystal defects and chemical order/disorder such as grain boundaries, anti-phase boundaries, stacking faults, dislocations and point defects, and to precisely localize the 3D coordinates of individual atoms in materials without assuming crystallinity. As coherent X-ray sources and powerful electron microscopes are under rapid development in the world, it is anticipated that CDI and AET will find broad applications across different disciplines.
June 8, 2017 Raphael Flauger - University of California, San Diego Deciphering the Beginning The cosmic microwave background contains a wealth of information about cosmology as well as high energy physics. It tells us about the composition and geometry of the universe, the properties of neutrinos, dark matter, and even the conditions in our universe long before the cosmic microwave background was emitted. After a general introduction, I will discuss lessons from the recently released Planck full mission data for models of the early universe. Finally, I will turn to the search for primordial gravitational waves and provide an outlook what we may hope to learn from current and future CMB experiments. Video
May 25, 2017 Rob Myers - Perimeter Institute Scanning New Horizons: Information, Holography & Gravity New advances and insights often emerge from the confluence of different ideas coming from what appeared to be disconnected research areas. The theme of my talk will review an ongoing collision between the three topics listed in the title above which has been generating interesting new insights about the nature of quantum gravity, as well as other fields, eg, condensed matter physics and quantum field theory. Video
May 18, 2017 Rychard Bouwens - Leiden University Young Galaxies Forming in the High-Redshift Universe Over the last few years, enormous progress has been made in studying galaxies in the first two billion years thanks to the incredible capabilities of the Hubble and Spitzer Space Telescopes. Already, more than 1500 probable galaxies are known at redshifts above z~6, and now the current frontier is at z~9-10, with 50 plausible galaxy identifications to date, and a spectroscopic redshift measurement to z=11.1. Noteworthy advances are also being made in characterizing the physical properties of these distant galaxies, with probes of the nebular emission lines and specific star formation rates to z~8.5 and new constraints on dust-enshrouded star formation at z>~2 from ALMA. One area where there has been particularly exciting activity is in the study of ultra-faint galaxies in the early universe with the Hubble Frontier Fields (HFF) program, combining the power of long exposures with Hubble and Spitzer with gravitational lensing by massive galaxy clusters. In this colloquium, I survey these and other highlights of current research on high redshift galaxies, while looking forward to future work with JWST. Video
May 11, 2017 Daniel Whiteson - University of California, Irvine Deep Learning in High Energy Physics Recent advances in artificial intelligence offer opportunities to disrupt the traditional techniques for data analysis in high energy physics. I will describe the new machine learning techniques, explain why they are particularly well suited for particle physics, and present selected results that demonstrate their new capabilities. Video
May 4, 2017 Oleg Gnedin - University of Michigan Progress in Simulations of Galaxy Formation I will discuss recent progress in numerical modeling of galaxy formation. Cosmological simulations can now resolve galactic structure on the spatial scale of parsecs, and follow the build-up and dissociation of giant molecular clouds. A lot of effort is going into understanding the drivers of turbulence in the interstellar medium and the effects of young stars. I will present a novel approach to modeling galactic star formation as a composition of individual star clusters, which allows new powerful tests of galaxy formation simulations. In a few years we should have fairly reliable predictions for full star formation histories of galaxies. Video
April 27, 2017 Sima Setayeshgar - Indiana University Optimal strategies in single cell sensing and response Biochemical reactions constitute the cell's computing language, carrying out the processes of life from cell growth and death to response to environmental cues. In a classic work, Berg and Purcell showed that bacterial chemotaxis, where a single-celled organism responds to small changes in the concentration of chemicals outside the cell, is limited directly by molecule counting noise and that aspects of the bacteria's computational and behavioral strategies are optimal given the physical constraints. In this talk, I will revisit and extend their arguments: For the ubiquitous case of sensing by multiple, cooperatively interacting biological receptors, I will show that while the sensiti?vity of response to the change in concentration of signaling molecules is enhanced, the accuracy is limited by the irreducible noise related to the random arrival of diffusing molecules. I will compare theoretical limits with quantitative experimental results for the bacterial flagellar motor demonstrating performance consistent with physical limits. I will also discuss related work aimed at understanding system-level properties of the chemotaxis signaling network from the standpoint of network adaptation and information transmission. Video
April 20, 2017 Yannick Meurice - University of Iowa Application of the tensor renormalization group method to quantum simulations and machine learning The renormalization group method has played a key role in establishing the standard model of electroweak and strong interactions. It connects the short and large distance behaviors of field theoretical models and provides an unified way to approach lattice models in condensed matter and high energy physics. I describe a recently proposed computational method called tensor renormalization group which applies to spin and gauge models. I discuss applications in the context of quantum simulations on optical lattice and machine learning. Video
April 13, 2017 Michael Roukes - Caltech Nanotechnology for Massively-Parallel, Multi-Physical Interrogation of Brain Activity Although our understanding of the properties of individual neurons and their role in brain computations has advanced significantly over the past several decades, we are still far from elucidating how complex assemblies of neurons – that is, brain circuits – interact to process information. In 2011, six U.S. scientists from different disciplines banded together, outlined a vision [1,2], and managed to convince the Obama administration of the unprecedented opportunity that exists to launch a coordinated, large-scale international effort to map brain activity. This culminated in the U.S. BRAIN Initiative (Brain Research through Advancing Innovative Neurotechnologies), which was launched in 2013. Our perspective was predicated, in part, on the current level of maturity of diverse fields of nanotechnology and silicon very-large-scale integration (VLSI) that can now be coalesced to create unprecedented tools for massively parallel interrogation of brain activity. We will outline the immense complexity of such pursuits, the hopes we articulated, survey the existing technological landscape for assembling the requisite instrumentation, and then focus upon our own collaborative efforts toward tools enabling multi-physical interrogation of brain activity. We believe this technology will engender a spectrum of new possibilities for neuroscience and clinical neuromedicine.
April 6, 2017 Kai Mueller - Technical University of Munich Nanostructure Quantum Photonics Optically active semiconductor nanostructures are promising candidates for building blocks in future photonic quantum technologies, including quantum information processing, quantum communication, quantum sensing and quantum metrology. By embedding a single quantum emitter inside a nanoresonator that strongly localizes the optical field, it is possible to achieve a very strong light–matter interaction. The strength of this interaction is characterized by the coherent emitter-field coupling strength (g), which increases with reduction in the optical mode volume and which also sets the limit on the operational speed of such a system. With InAs quantum dots inside GaAs photonic crystal cavities, coupling strengths of 40 GHz can be reached (much greater than the record values in atom-cavity QED systems). This allows the system to be operated in the strong coupling regime where the formation of hybridized light-matter states results in effective photon-photon interactions and enables the on-chip generation of nonclassical light [1-2]. Exploiting interference effects which are intrinsic to the photonic crystal platform [3] allows to significantly improve the signal to noise ratio and enables the on-chip generation of indistinguishable photons with state-of-the-art metrics [4]. Finally, I will discuss possibilities for generating nonclassical states of light beyond single photons, such as photon bundles. Specifically, I will show that resonantly driven two-level systems which are well established as single-photon sources can also act as sources of two-photon pulses [5].
March 16, 2017 Leslie Rosenberg - University of Washington Searching for Dark-Matter Axions The axion is a hypothetical elementary particle whose existence would explain the baffling absence of CP violation in the strong interactions. Axions also happen to be a compelling dark-matter candidate. Axions could comprise the overwhelming majority of mass in the universe, yet they would be extraordinarily difficult to detect. However, several experiments, either under construction or in operation, would be sensitive to even the more pessimistically coupled dark-matter axions. This talk reviews the state of these searches. Video
March 9, 2017 Elena Pierpaoli - USC The Cosmos seen through the Planck satellite eyes The Cosmic Microwave Background (CMB) radiation allows us to study processes of the very early Universe. The detailed study of its anisotropies with the Planck satellite allowed to determine cosmological parameters at unprecedented level of precision. As a byproduct, it also provided important results in several areas of astrophysics such as the detection of clusters through their Sunyavev-Zeldovich signature and characterization of Galactic emission at microwave and infrared wavelengths. The Planck satellite, which was launched in 2009, has completed collecting data and most results have recently been released. I will review the main achievements of the latest data release and interpretation, including the determination of main cosmological parameters, epoch of star formation, galaxy clusters detection and use. I will also discuss future prospects in CMB studies. Video
March 2, 2017 Christoph Haselwandter - USC Physical Mechanisms of Membrane Protein Organization and Collective Function Cell membranes are one of the fundamental hallmarks of life. For many of their biological functions, cell membranes rely on the collective properties of lattices of interacting membrane proteins. Here we explore the general physical mechanisms and principles underlying supramolecular organization and collective function of membrane proteins, based on three model systems: (1) We show how the interplay of protein-induced lipid bilayer curvature deformations, topological defects in protein packing, and thermal effects can explain the observed symmetry and size of membrane protein polyhedral nanoparticles; (2) We predict that the observed four- and five-fold symmetric states of mechanosensitive ion channels yield characteristic lattice architectures of channel clusters, with distinctive collective gating properties; (3) We show that lipid bilayer-mediated elastic interactions between chemoreceptor trimers provide a physical mechanism for the observed self-assembly of chemoreceptor lattices, and may contribute to the cooperative signaling response of the chemotaxis system. Video
February 23, 2017 Harry Nelson - UCSB Touch the Dark Matter We know from astrophysical evidence that the vast majority of matter in our Universe neither absorbs nor emits light. Does this Dark Matter' have any relation to the strong, electromagnetic, or weak interactions that comprise our Standard Model' of particle physics? I'll discuss the current & future world program to detect the dark matter in terrestrial experiments, with particular emphasis on the intense competition among experiements that utilize liquid xenon. The flagship US dark matter experiment, LZ, is part of that competition, and just received final Department of Energy approval. Video
February 16, 2017 Nathaniel Craig - UCSB Is Nature Natural? The discovery of the Higgs boson at the LHC marks the culmination of a decades-long quest for the final piece of the Standard Model. But the discovery of the Higgs also adds new urgency to the hierarchy problem, namely the question of why the Higgs boson is so light despite its unique quantum sensitivity to much higher energy scales. This puzzle is made all the more challenging by the lack of evidence for conventional approaches to the hierarchy problem at the LHC and other experiments. In this talk I'll discuss the essential features of the hierarchy problem and its possible solutions, with a particular focus on new approaches to the problem that have emerged in the years following the Higgs discovery. These new approaches feature novel experimental signatures, add urgency to the measurement of Higgs properties, and may shed light on dark matter and other mysteries of the Standard Model. Video
February 9, 2017 ALice Shapley - UCLA The MOSFIRE Deep Evolution Field (MOSDEF) Survey: A Detailed Census of the Physics of Galaxy Formation in the Early Universe Understanding the formation and evolution of galaxies remains one of the great challenges of modern cosmology. Key outstanding questions include: What are the physical processes driving the formation of stars in individual galaxies? How do galaxies exchange material with their intergalactic environments? How do the impressive variety of galactic structures that we observe today assemble? How do supermassive black holes affect the evolution of their host galaxies? We present new results from the MOSFIRE Deep Evolution Field (MOSDEF) survey, a comprehensive census of the galaxy population during the peak epoch of activity in the universe ~10 billion years ago. In addition to providing an overview of the MOSDEF survey and its science, we focus on new results regarding the evolving physical conditions in star-forming regions towards higher redshift. Our new results suggest many exciting future observational directions for untangling the detailed nature of star formation in the early universe. Video
February 2, 2017 Hendrik Ohldag - Stanford Synchrotron Radiation Laboratory Ultrafast and Very Small: Discover Nanoscale Magnetism With Picosecond Time Resolution Using X-Rays Today’s magnetic device technology is based on complex magnetic alloys or multilayers that are patterned at the nanoscale and operate at gigahertz frequencies. To better understand the behavior of such devices one needs an experimental approach that is capable of detecting magnetization with nanometer and picosecond sensitivity. In addition, since devices contain different magnetic elements, a technique is needed that provides element-specific information about not only ferromagnetic but antiferromagnetic materials as well. Synchrotron based X-ray microscopy provides exactly these capabilities because a synchrotron produces tunable and fully polarized X-rays with energies between several tens of electron volts up to tens of kiloelectron volts. The interaction of tunable X-rays with matter is element-specific, allowing us to separately address different elements in a device. The polarization dependence or dichroism of the X-ray interaction provides a path to measure a ferromagnetic moment and its orientation or determine the orientation of the spin axis in an antiferromagnet. The wavelength of X-rays is on the order of nanometers, which enables microscopy with nanometer spatial resolution. And finally, a synchrotron is a pulsed X-ray source, with a pulse length of tens of picoseconds, which enables us to study magnetization dynamics with a time resolution given by the X-ray pulse length in a pump-probe fashion. The goal of this talk is to present an introduction to the field and explain the capabilities of synchrotron based X-ray microscopy, which is becoming a tool available at every synchrotron, to a diverse audience. The general introduction will be followed by a set of examples, depending on the audience, that may include properties of magnetic materials in rocks and meteorites, magnetic inclusions in magnetic oxides, interfacial magnetism in magnetic multilayers, and dynamics of nanostructured devices due to field and current pulses and microwave excitations. Video
January 19, 2017 Xiaoping Hu - UCR MRI: A Field with Endless Advances and Diverse Biomedical Applications Although MRI was invented more than 40 years ago and has been a routine diagnostic imaging modality in clinical practice for more than 30 years, it is still an area of active research with advances being continuously made. These advances have been brought about by technological developments and introduction of new biomedical applications. This talk will provide a brief review major milestones in MRI and highlight some recent advances, particularly those related to neuroimaging. Video
January 12, 2017 Mark Alber - UCR Combined Multi-scale Computational and Experimental Studies of Bacterial Swarming and Blood Clot Formation Surface motility such as swarming is thought to precede biofilm formation during infection. Population of bacteria P. aeruginosa, major infection in hospitals, will be shown to efficiently propagate as high density waves that move symmetrically as rings within swarms towards the extending tendrils. Multi-scale model simulations suggest a mechanism of wave propagation as well as branched tendril formation at the edge of the population that depend upon competition between the changing viscosity of the bacterial liquid suspension and the liquid film boundary expansion caused by Marangoni forces. This collective mechanism of cell-cell coordination was shown to moderate swarming direction of individual bacteria to avoid antibiotics. In the second half of the talk, a novel three-dimensional multi-scale model will be described for simulating receptor-mediated adhesion of deformable platelets at the site of vascular injury under different shear rates of blood flow. The modeling approach couples submodels at three biological scales crucial for the early clot formation: novel hybrid cell membrane submodel to represent physiological elastic properties of a platelet, stochastic receptor–ligand binding submodel to describe cell adhesion kinetics and lattice Boltzmann submodel for simulating blood flow. Predictive model simulations revealed that platelet deformation, interactions between platelets in the vicinity of the vessel wall as well as the number of functional GPIba platelet receptors played significant roles in platelet adhesion to the injury site. Lastly, macro-scale model of blood clot deformation and deformation of blood vessel will be described. The model represents clot as a ternary complex fluid made of heterogeneously distributed platelets, fibrin network and plasma phases and takes into account mechanical properties of different phases. Video
December 1, 2016 Dr. Zvi Bern - UCLA A curious story of quantum gravity in the ultraviolet For the past 30 years nearly all theoretical physicists have believed that quantum field theories based on Einstein's general relativity necessarily must be ill-defined in the ultraviolet. This is the well known nonrenormalizability problem of gravity. But is it actually true, in general? We describe recent calculations that cast doubt on this simple picture and show that quantum gravity is much tamer in the ultraviolet than believed possible. The new calculations make use of enormous advances in our ability to compute scattering amplitudes in quantum field theory by relating gravity theories to gauge theories. Applications to black holes will be mentioned.  Video
November 17, 2016 Dr. Boris Shraiman - KITP Physics and Biology of Morphogenesis One hundred years ago, D'Arcy Thompson – a nineteenth century polymath, working at the turn of the twentieth century – wrote a monograph, "On Growth and Form", in which he pondered the geometry of living forms and how it emerges in the process of Morphogenesis. Thompson was ahead of his time. Since then, progress of Developmental Biology and Molecular Genetics uncovered many if not most of key genes and molecules involved in Morphogenesis, yet Thompson's agenda of understanding how developmental processes actually specify the geometry of tissues, limbs and organs is far from complete. A particular challenge is to bridge the gap between microscopic scales, where molecular mechanisms operate, and the macroscopic scales of animal "shape and form". This challenge offers much for a Physicist to think about. This talk will focus in particular on the mechanical aspects of morphogenesis i) examining the role of mechanical stress in regulation of growth and ii) seeking a quantitative understanding of tissue flows observed in morphogenesis. At the interface of Physics and Biology we will find some new biology and new physics.  Video
November 10, 2016 Dr. Rui-Rui Du - Rice Electronic Superhighway in Topological Insulators Electrical insulators commonly refer to the materials that prevent the flow of electricity. However, recent research demonstrates a type of topological insulators which has novel properties. Although electricity cannot flow through them, it can flow around their narrow outer edges. The material, called a "quantum spin Hall topological insulator", acts as an electronic superhighway. It is one of the building blocks needed to create future electronics and computers. In this talk I will show such insulators can be built from common compound semiconductors containing a double-layer of electrons and holes, which are created by band-gap engineering using molecular beam epitaxy and electrostatic gates. The material supports quantized helical edge modes. Amazingly, due the interactions between electron and holes, the material can become a superconductor, where the pairing of electron and holes resembles the Cooper pair in ordinary superconductors.  Video
November 3, 2016 Dr. Ehud Altman - Berkeley Ergodicity, entanglement and many-body localization in quantum dynamics. Do quantum many-body systems necessarily come to thermal equilibrium after a long enough time evolution? The conventional wisdom has long been that they do and that, in the process, any quantum information encoded in the initial state is lost irretrievably. Thus the dynamics of many interacting particles becomes effectively classical. But these ingrained notions of thermalization and ergodicity have recently been called into question. In this talk I will discuss how ergodicity can break down in disordered quantum systems through the phenomenon of many-body localization. In contrast to thermalizing fluids, quantum correlations can persist through time evolution of the localized state even at high energy densities. Thus, investigating the many-body localization transition offers a concrete route to address fundamental unsolved questions concerning the boundary between classical and quantum physics in the macroscopic world. I will emphasize the important role that quantum entanglement plays in current attempts to understand this fascinating dynamical phase transition. Finally I will present recent progress in confronting the emerging theoretical understanding of many-body localization with experimental tests using systems of ultra-cold atoms.  Video
October 27, 2016 Dr. Barry Barish - Caltech LIGO and the Detection of Gravitational Waves Einstein predicted the existence of gravitational waves 100 years ago. They have been recently observed from pairs of merging Black Holes by the Laser Interferometer Gravitational-wave Observatory (LIGO). The physics of gravitational waves, the detection technique, the observations, including latest results, and implications will all be discussed.  Video
October 13, 2016 Stephen Kane - San Francisco State University Analyzing Alien Worlds: A Multidisciplinary Approach to Characterizing Exoplanets About the Speaker: Stephen Kane has been researching planets orbiting other stars for more than 20 years. He has discovered and characterized hundreds of exoplanets, including Kepler-186f, which is the smallest planet yet found in the Habitable Zone of a star. After spending many years working at the NASA Exoplanet Science Institute, Kane is now an Associate Professor of Astrophysics at San Francisco State University (SFSU). He is the Chair of the Kepler Habitable Zone Working Group and the Director of the Planetary Research Laboratory at SFSU. Stephen is involved in several upcoming and ongoing NASA missions in ways that dovetail seamlessly with the UCR-based team of the NASA Astrobiology Institute. His work with the Deep Space Climate Observatory is the first major effort to use Earth's rotation and albedo to model modern Earth as an exoplanet. He is also leading a project to use the future James Webb Space Telescope to detect evidence for volcanic activity on terrestrial planets discovered with TESS, the Transiting Exoplanet Survey Satellite scheduled for launch in 2017. Abstract: The number of exoplanet discoveries has increased dramatically over the past several decades, requiring a planetary classification system to encompass the enormous diversity among worlds. Exoplanetary science can be broadly divided into categories of detection, characterization, and habitability. Kane's research has allowed him to address leading questions in all three areas: detecting multi-planet systems, determining the stability of planetary orbits, analyzing planetary atmospheres, and predicting the effects of both planetary orbit and geological activity on habitability. In this seminar, he will present highlights from his survey of potentially transiting exoplanets and his role in recent exoplanet discoveries. He will also present the results from his newly published catalog of Kepler planets in the habitable zones of their host stars and describe the methodology he developed for distinguishing between Earth and Venus analogs. Finally, he will describe future opportunities from both ground and space-based observatories that will be used to provide a more complete understanding of comparative planetology.
October 6,2016 Jesse Thaler - MIT New Physics Gets a Boost: Jet Substructure at the Large Hadron Collider Collisions at the Large Hadron Collider (LHC) are dominated by jets, collimated sprays of particles that arise from quantum chromodynamics (QCD) at high energies. With the remarkable performance of the ATLAS and CMS detectors, jets can now be characterized not just by their overall direction and energy but also by their substructure. In this talk, I highlight the increasingly important role that jet substructure is playing in searches for dark matter and other new physics at the LHC, especially when exploring extreme kinematic regimes involving large Lorentz boosts. I also explain how innovative theoretical studies of jet substructure have taught us surprising lessons about QCD, revealing new probes of hot dense matter and universal features of gauge theories.
September 29, 2016 DR. Samindranath Mitra - PRL Editor Physics after the lab and the desk: Your work in PRL Physics research takes place mostly at your desk, at the keyboard, in the lab. You communicate results through posters, talks, and papers -- leading to, hopefully, wide dissemination and recognition. This sequence entails interacting with journal editors, referees, conference chairs, journalists, and so on. I will focus on this post-research collaborative process in physics, primarily through the lens that is Physical Review Letters.
September 22, 2016 Dr. Brian Siana - UCR Dwarf Galaxies in the Early Universe: Finding and Characterizing the Other Half of Star Formation Small galaxies in the early universe are incredibly important. They comprise the majority of early star formation, reionized the hydrogen in the intergalactic medium and populated it with heavier elements. Furthermore, mysteries about the abundance and dynamics of dwarf galaxies today may be giving insights into the properties of dark matter or, alternatively, may arise from baryonic process during early star formation episodes. To understand these star formation episodes, we first have to see the dwarf galaxies. I will summarize our research using gravitational lenses to get a census of these previously unobservable dwarf galaxies, and to better characterize their star formation histories and ionizing emission.
June 2, 2016 Henri Orland - CEA- Saclay, Paris Pseudoknots and knots in RNA After reviewing some elementary properties of RNA, we recall how secondary structures of RNA without pseudoknots can be computed using simple concepts of statistical physics. The situation is much more complex when dealing with RNA structures with pseudoknots. In that case, inspired by matrix field theory, we introduce a classification of pseudoknots in terms of their topological genus. The standard free energy parametrization is modified to include a penalty proportional to the genus of the RNA structure, and we present two algorithms to efficiently predict RNA structures with pseudoknots. In the last part of the talk, we address the question: Are there knots in RNA? To try to answer this question, we present a thorough study of the database of all known RNA structures.
May 26, 2016 Harry Teplitz - IPAC Infrared Grism Spectroscopy from Space: Hubble Results and Preparing for New Missions Slitless grism spectroscopy is an efficient way for space telescopes to obtain large samples of low resolution spectra in the near infrared wavelength range. The Hubble Space Telescope’s Wide Field Camera 3 (WFC3) offers a powerful example of this technique. I will review current results from WISPs (WFC3 Infrared Spectroscopic Parallel survey), which observes “random” parallel fields 5 to 8 arcminutes away from primary observations taken by other instruments. The WISPs dataset includes almost 2000 hours of HST data, which have led to a range of discoveries in the study of galaxy evolution. In addition, WISP is the ideal pathfinder for planning the future WFIRST and Euclid missions, which will both employ near infrared grisms over thousands of square degrees of the extragalactic sky.
May 19, 2016 Laura Sales - UCR Dwarf galaxies and their satellites as extreme probes of LCDM The cosmological scenario (Lambda Cold Dark Mater, LCDM) makes three clear predictions for the dark matter halos surrounding galaxies: 1) the number of halos steeply rises towards low-mass objects, 2) halos are "cuspy" at their centers and 3) there should be a wealth of substructure swarming around each of these halos. We use cosmological numerical simulations of halos and galaxies to explore these predictions and to compare them with available observational constraints, such as the Baryonic Tully-Fisher relation and the inventory of dwarfs (low-mass galaxies) in the Local Volume. The recent detection of several dwarf galaxies potentially associated with the Magellanic Clouds is an exciting discovery that confirms that the hierarchical nature of galaxy formation extends down to the faintest limits probed, just as predicted by LCDM. On the other hand, the extreme baryon content of some isolated dwarfs together with the large variety of rotation curve profiles for these objects presents a newly recognized challenge to the paradigm that still awaits resolution. Do we need to move beyond Cold Dark Matter?
May 12, 2016 Arjun Dey - NOAO Mapping the Universe: A New Generation of Sky Surveys The Dark Energy Spectroscopic Instrument project, which will begin operations in 2019, will measure the expansion history of the universe to unprecedented precision and provide sub-percent constraints on the distance scale and the equation of state of dark energy. I will describe the current state of the project and the wide-field imaging surveys that are being undertaken in preparation for the DESI spectroscopic survey. These imaging surveys are using state-of-the-art red-sensitive cameras and will benefit a wide range of astrophysical studies. The data sets being created will have lasting legacy value, well into the LSST era.
May 5, 2016 Tony Tyson - UC Davis LSST and the physics of the dark universe The physics that underlies the accelerating cosmic expansion is unknown. This, "dark energy" and the equally mysterious "dark matter" comprise 96% of the mass-energy of the universe and are outside the standard model. Recent advances in optics, detectors, and information technology, has led to the design of a facility that will repeatedly image an unprecedented volume of the universe: LSST. For the first time, the sky will be surveyed wide, deep and fast. The history of astronomy has taught us repeatedly that there are surprises whenever we view the sky in a new way. I will focus on the technology of LSST, and review several independent probes of the nature of dark energy and dark matter. These new investigations will rely on the statistical precision obtainable with billions of galaxies.
April 28, 2016 Kirill Shtengel - UCR Anyonics: Exotic circuitry with anyons, or how to build a Flux Capacitor Anyons (particularly non-Abelian anyons) are widely sought for the exotic fundamental physics they harbour as well as for their possible applications for quantum information processing. Currently, there are numerous blueprints for stabilizing the simplest type of non-Abelian anyon, a Majorana zero energy mode bound to a vortex or a domain wall. One such candidate system, a so-called "Majorana wire" can be made by judiciously interfacing readily available materials; the experimental evidence for the viability of this approach is presently emerging. Following this idea, we introduce a device fabricated from conventional fractional quantum Hall states, s-wave superconductors and insulators with strong spin-orbit coupling. Similarly to a Majorana wire, the ends of our “quantum wire” would bind "parafermions", exotic non-Abelian anyons which can be viewed as fractionalized Majorana zero modes.I will briefly discuss their properties and describe how such parafermions can be used to construct new and potentially useful circuit elements which include current and voltage mirrors, transistors for fractional charge currents and "flux capacitors".
April 21, 2016  Daniel Cox - UC Davis Proteins as Molecular Legos: How Lessons Learned from Mad Cow Disease can be Applied to Novel Materials and Biotechnology The unregulated yet ordered self-assembly of large disordered proteins such as prion and tau contribute to neurodegenerative diseases like mad cow and Alzheimer’s. Nevertheless, organisms as diverse as yeast, spiders, lacewings, and E. coli bacteria have evolved mechanisms to harness these protein aggregation processes for their benefit, using the proteins effectively as “Molecular Legos”. In this talk I will discuss how related “beta solenoid” proteins can be engineered to undergo this self-assembly in a controlled way to produce remarkably stable and beautifully ordered structures that can be harnessed for nanotechnology and biotechnology applications including energy harvesting and biosensing. I will discuss the physics of the aggregation process, how you can measure it with Rayleigh scattering, and how you can measure the mechanical toughness with both computer simulations and high intensity ultrasound. We find that the filaments of our engineered beta solenoid proteins are stiff against bending and twist, and have a mechanical toughness comparable to Kevlar.
April 14, 2016 Bharat Ratra - Kansas State University Dark Energy: constant or time variable? (... and other open questions) Experiments and observations over the last two decades have persuaded cosmologists that (as yet undetected) dark energy is by far the main component of the energy budget of the universe. I review a few simple dark energy models and compare their predictions to observational data, to derive dark energy model-parameter constraints and to test consistency of different data sets. I conclude with a list of open cosmological questions.
April 7, 2016 Alex Rudolph - California State Polytechnic University CAMPARE and Cal-Bridge: Engaging Underrepresented Students in Physics and Astronomy The level of participation by underrepresented minority (URM) and female students in physics and astronomy PhD programs is shamefully low (2-4% for URM v. 30% in the general population; 20% for women v. 50% in the general population). I will begin by discussing research into why these participation rates are so low for these groups, highlighting role the physics and general GRE tests play in suppressing diversity in our field, while providing little to no benefit in helping predict long-term success. I will then describe some alternative methods of conducting graduate admissions, including the role of programs like Cal-Bridge and CAMPARE. I will then describe these two California-wide, multi-institutional programs, CAMPARE and Cal-Bridge, with the common mission of increasing participation of underrepresented minorities and women in astronomy and physics through summer research opportunities, in the case of CAMPARE, scholarships in the case of Cal-Bridge, and significant mentoring and professional development in both programs, leading to an increase in their numbers completing bachelor’s degrees, and successfully pursuing a PhD in these fields. There are plans for an expansion of the Cal-Bridge program to include students interested in physics PhDs, as well as to make it statewide. I will be talking about how UCR physics and astronomy faculty can get involved in the program and these expansion efforts.
March 31, 2016 Joshua Lui - UCR Shedding light on two-dimensional electrons in graphene and beyond Graphene, a single layer of carbon atoms, has stimulated intense scientific interest due to its distinctive electronic and mechanical properties. Graphene exhibits strong interactions with light over a broad spectral range. This enables us to examine its electronic and vibrational properties through optical spectroscopy. In addition to gaining understanding of the properties of single-layer graphene, we can also probe the behavior of electrons in few-layer graphene. This reveals the unique electronic and vibrational properties for graphene of each layer thickness and stacking order, as well as their distinct capability to induce an electrically tunable band gap. I will also highlight recent development of 2D materials beyond graph
March 10, 2016 Evan Kirby - Caltech Dwarf Galaxies: Laboratories for Nucleosynthesis and Dark Matter The Milky Way is surrounded by dozens of dwarf galaxies. Although these galaxies contain as few as 1000 stars (compared to 100 billion stars in the Milky Way), they have masses equivalent to millions of stars. The extra mass suggests that dwarf galaxies are reservoirs for dark matter.
March 3, 2016 Micahel M. Fogler - UC San Diego Hyperbolic waves in Nature: from nano to Terra Waves with hyperbolic dispersion relation are exotic yet surprisingly widespread phenomena that occur in anisotropic media with internal resonances. Such media have been investigated in numerous fields, ranging from engineering to condensed matter physics to optics to fluid dynamics and geophysics. Hyperbolic waves can be found in magnetic materials, in both usual and topological insulators, in superconductors, as well as in our oceans, beaches, atmosphere, and space. The characteristic lengths and frequencies of such waves vary vastly, from atomic to cosmic. However, they all exhibit certain common attributes, such as strict directionality, diverging density of states, and anomalous reflection. This talk will contain a primer on hyperbolic materials, a recipe for a death ray, and a report on our nano-optics studies of hyperbolic phonon-polaritons in new quasi-2D materials such as graphene and hexagonal boron nitride.
February 25, 2016 Jim Olsen - Princeton University Dispatches from the Energy Frontier: Latest results from the Large Hadron Collid In May, 2015 the Large Hadron Collider (LHC), the world’s highest energy particle collider, resumed operations after a two year shutdown. The downtime was used to prepare the machine and detectors for proton collisions at higher energy and intensities than have ever been achieved before. Following the discovery of the Higgs boson in 2012, which led to the awarding of the Nobel Prize in Physics to Peter Higgs and Rene Englert, the primary focus on the two large experiments, ATLAS and CMS, operating at the LHC is to search for signs of new particles or interactions that could either shed light on unexplained mysteries of the Standard Model of particle physics, or even provide evidence of unexpected phenomena not previously predicted. One interesting example of such a scenario was recently reported by ATLAS and CMS, where both experiments see an excess of events containing two photons that could be the first hint of a new particle with a mass near 750 GeV. In this colloquium I will present recent results from the LHC, including the diphoton excess and searches for supersymmetric particles and other exotic phenomena, as well as a host of new measurements establishing the Standard Model at the unprecedented energy of 13 TeV. I will close with a brief outlook on expectations for the LHC in the near and long term.
February 18, 2016 Marusa Bradac - UC Davis Dark Matter and First Galaxies Light Up The Bullet Cluster has been the subject of intense research in the last few years. This system is remarkably well-suited to addressing outstanding issues in both cosmology and fundamental physics. I will present measurements of the composition of this system, show the evidence for existence of dark matter, and describe limits that we placed on the intrinsic properties of dark matter particles. I will also present results from a much larger sample of Bullet-like clusters, MACSJ0025-1222, A520, and DLSCL J0916.2+2951 among others.
February 11, 2016 Itai Cohen - Cornell University Flight of the Fruit Fly There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature’s most accomplished aviators - the fly. If however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? Despite pioneering studies of flight control in tethered insects, robotic wing experiments, and fluid dynamics simulations that have revealed basic mechanisms for unsteady force generation during steady flight, the answers to these questions remain elusive. In this talk I will discuss our strategy for investigating these unanswered questions. I will begin by describing our automated apparatus for recording the free flight of fruit flies and our technique called Hull Reconstruction Motion Tracking (HRMT) for backing out the wing and body kinematics. I will then show that these techniques can be used to reveal the underlying mechanisms for flight maneuvers, wing actuation, and flight stability. Finally, I will comment on the implications of these discoveries for investigations aimed at elucidating the evolution of flight.
February 4, 2016 Dan Stark - University of Arizona Galaxies in the Reionization Era Deep infrared images from the Hubble and Spitzer Space Telescopes have recently pushed the cosmic frontier back to just 500 million years after the Big Bang, delivering the first large sample of galaxies at redshifts between 7 and 10. Sometime in this redshift window the hydrogen in the intergalactic medium transitioned from mostly neutral to ionized. Over the past five years, our understanding of this process of reionization has improved greatly. The census of early galaxies derived from deep Hubble imaging has provided new insight into the role of star forming galaxies in driving reionization, while follow-up spectroscopy has constrained the timescale over which the transition happened. Most recently, deep MOSFIRE spectra have begun to provide the first glimpse of the physical nature of early galaxies, hinting at a very different population from what has been observed at lower redshifts. I will review the latest progress in our understanding of the first billion years of cosmic history and discuss the remaining challenges that must be addressed in advance of JWST.
January 28, 2016 Mlke Roney - University of Victoria Applying Quantum Entanglement to Search for New Physics at TeV Energies Collisions of electrons and positrons can create B-meson particles in an entangled state. I will explain how the BABAR experiment has applied the associated Einstein–Podolsky– Rosen effect to study differences between matter and antimatter known as CP violation, as well as how it has used the effect to observe the “quantum arrow of time”. The Belle II/SuperKEKB facility that is currently being commissioned in Japan will extend these studies and will be sensitive to new physics at energies well above those available at the Large Hadron Collider. I will describe how it will do so and investigate the evidence for new physics published by BABAR and recently corroborated by the Belle and LHCb experiments.
January 21, 2016 Tony Heinz - Departments of Applied Physics and Photon Science, Stanford University Two-Dimensional Materials - Graphene and Beyond Graphene, a single atomic layer of carbon atoms, has attracted great attention worldwide because of its potential for novel science and technology. Recently, this interest has expanded to the much wider class of two-dimensional materials that occur naturally as 2D layers of van-der-Waals crystals. While preserving graphene’s flexibility and tunability by external perturbations, atomically thin layers of this broader set of materials provides access to more varied electronic and optical properties, including semiconducting and insulating behavior. In our presentation, we will discuss the distinctive properties of these atomically thin 2D materials, emphasizing how they can be probed by light. For the prototypical system of graphene, the electronic response has been investigated from the THz to the UV, revealing many interesting physical properties of 2D Dirac fermions. Atomically thin layers of semiconductors in the family of transition metal dichalcogenides (MX2 where M = Mo, W and X = S, Se, Te) have also been investigated. Although weak light emitters as bulk crystals, at monolayer thickness these materials emit light efficiently. We will describe some of the surprising characteristics exhibited by these materials in the 2D limit, from their strong and anomalous excitonic effects to valley selective excitation and control.
January 14, 2016 Bertrand Echenard - Caltech The Mu2e experiment: finding a needle in a trillion haystacks The Mu2e experiment at Fermilab will be the world's most sensitive search for neutrinoless muon-to-electron conversion, a charged lepton-flavor violating process. Although neutral lepton-flavor violation has been clearly established in the neutrino sector, no sign of charged lepton-flavor violation has been detected so far, despite decades of experimental searches. An observation would constitute an unambiguous sign of physics beyond the standard model, and severely constrain new theoretical models. The Mu2e experiment will improve the current sensitivity to muon-to-electron conversion by four orders of magnitude, and indirectly probe energy scales well beyond the reach of the LHC.
January 7, 2016 Henk Postma - Cal State Northridge Towards rapid sequencing of individual DNA molecules with graphene nanogaps I will describe our lab's latest efforts in realizing a graphene nanogap device that may be used for sequencing individual DNA molecules. The technique is based on reading the base sequence of a single DNA molecule using a graphene nanogap to read the DNA’s transverse conductance. Because graphene is a single atom thick, single-base resolution of the conductance is readily obtained. The nonlinear current-voltage characteristic is used to determine the base type independent of nanogap-width variations that cause the current to change by 5 orders of magnitude. The expected sequencing error rate is 0% up to a nanogap width of 1.6 nm.
December 3, 2015 James Bullock - UCI Dwarf Galaxies, the Local Group, and Cosmology The Local Group and the tiny galaxies that surround the Milky Way provide unique and detailed data sets for testing ideas in cosmology and galaxy formation. In this talk I will discuss how numerical simulations coupled with local "near-field" observations are informing our understanding of dark matter, the formation of the first galaxies, and the physical processes that act at the threshold of galaxy formation.
November 19, 2015 DR. Thorsten Emig - MIT and CNRS Paris Geometrically constrained fluctuations The modification of (quantum and thermal) fluctuations due to geometrical constraints give rise to a plethora of effects in equilibrium and non-equilibrium systems. Prominent examples include QED and critical Casimir interactions between macroscopic bodies, van der Waals forces between atoms and surfaces, and heat radiation and transfer. I shall review recent theoretical and experimental progress in the field, with applications extending from nano-systems over soft matter to urban physics.
November 12, 2015 John Chalker - Oxford Geometrically frustrated magnets and spin liquids Magnetic materials and theoretical models of them provide standard paradigms in condensed matter physics for the idea of ordering, in which interactions lead to a limited number of symmetry-related low-temperature states. Geometrical frustration is interesting as a way of making something different happen. Frustrated magnets have interactions that compete with each other, and they fluctuate between many different states even at low temperature. In this sense they provide an analogue for spin systems of the liquid phase of ordinary matter. Spin liquids, however, turn out to be much more interesting in important ways than ordinary liquids: in their low-energy states the microscopic magnetic moments are dissolved" by fluctuations and re-form as new degrees of freedom, often involving emergent gauge fields and fractionalised quasiparticles. I aim to present a simple overview of ideas in this field and to summarise some recent work on the dynamics of an exactly solvable model -- the Kitaev honeycomb model -- that has a spin liquid ground state.
November 5, 2015 Qian Niu - UT Austin Orbital Magnetism and Landau Levels A semiclassical theory of electron dynamics is derived which is accurate to second order in the magnetic field. We show how various geometric effects exhibit in the magnetic susceptibility as well as in the orbital magnetization. We also obtain a simple relation between the Landau level index and the magnetic response functions. One can thus obtain accurate Landau levels from first principles calculations, or measure the magnetic response functions from Landau level data.
October 29, 2015 Alan Rein - NCI Putting the Pieces Together: The Building Block of HIV-1 Virus Particles and How it is Assembled AIDS is caused by a virus called HIV-1. We will describe the replication cycle of the virus. A single virus-coded protein, “Gag”, is the building block of HIV-1 virus particles. We are studying the mechanisms by which several thousand Gag molecules are assembled into an “immature” HIV-1 particle and analyzing the structure of these particles. In a subsequent step in the viral life cycle, the Gag proteins in the immature particle are cleaved. These “maturation cleavages” result in a global reorganization of the particle and are absolutely required for viral infectivity. New results on a molecular switch triggering particle assembly will be presented.
October 22, 2015 Arun Paramekanti - U Toronto Band topology meets correlations - from solid state to cold atoms. The mathematics of topology plays an important role in many recently discovered effects in solid state matter, ranging from the quantum anomalous Hall effect to the quantum spin Hall effect and its higher dimensional generalizations. Recent work on cold atoms has also realized such physics by designing novel optical lattices and using lasers to create artificial orbital magnetic fields for neutral atomic gases. The interplay of such topological phases and interparticle interactions is a largely open field of research. The talk will give an introduction to this field and discuss some of our theoretical work, including the discovery of unusual forms of magnetism in spin-orbit coupled oxides and atomic gases, oxide heterostructures as platforms to realize quantum anomalous Hall phases, and emergence of novel phases at topological quantum critical points. more details» copy to my calendar
October 15, 2015 Chung-Pei Ma - UC Berkeley Supermassive Black Holes in Nearby Galaxies Black holes are among the most fascinating astrophysical objects and have long entranced the public. For over three decades, the giant elliptical galaxy Messier 87 has hosted the most massive known black hole in the local universe. New kinematic data and improved models in the past few years have substantially expanded and revised dynamical measurements of black hole masses at the centers of nearby galaxies. I will describe recent progress in discovering black holes beyond ten billion solar masses in ongoing surveys of massive elliptical galaxies. I will present updated scaling relations between the black hole mass and host galaxy properties, and discuss the implications for the formation of massive galaxies and the predicted gravity waves from merging supermassive black hole binaries.
October 8, 2015 Samir D Mathur - Ohio State Resolution of the black hole information paradox Some 40 years ago Hawking found a remarkable contradiction: if we accept the standard behavior of gravity in regions of low curvature, then the evolution of black holes will violate quantum mechanics. Resolving this paradox would require a basic change in our understanding of spacetime and/or quantum theory. In recent years the paradox has found an interesting resolution through string theory. While quantum gravity is normally expected to be important only at distances of order planck length, the situation changes when a large number N of particles are involved, as for instance in the situation where we make a large black hole. Then the length scale of quantum gravity effects grows with N, altering the black hole structure to a "fuzzball"; this effect resolves the paradox.
October 1, 2015 John Martinis - UCSB What’s next after Moore’s law: quantum computing As microelectronics technology nears the end of exponential growth over time, known as Moore’s law, there is a renewed interest in new computing paradigms. I will discuss recent research at UCSB on superconducting quantum bits, as well as our recent start at Google to build a useful quantum computer to solve machine learning problems. Two qubit experiments will be highlighted, one to simulate a chemical reaction that finds a cross section, and a second to extend the lifetime of a qubit state using quantum error correction.
June 4, 2015 Michael Rich - UCLA The Central Bulge of our Galaxy: New Insights and Mysteries Half of the light in the local Universe arises from the old stars in elliptical galaxies and bulges of spiral galaxies. At the center of our Galaxy lies a region called the "bulge" consisting of stars older and generally more metal rich than those in the disk, and hosting the Milky Way's central black hole. The central bulge population of our Milky Way is 700 times closer than the nearest similar stars in M31, providing a remarkable opportunity to learn the age, composition, kinematics, structure, and origin of this population. Present cold dark matter models suggest that the Milky Way and similar galaxies should have been bombarded by the infall of satellite galaxies during their lifetime and galaxies with bulges like that of our Milky Way would be predicted to not have survived in the form we observe today. I will discuss two new survey programs: one uses the Dark Energy Camera at the Cerro Tololo Observatory to image the central 1000 parsecs of the Milky way, and the other survey aims to measure the composition of giants just a few parsecs distant from the Milky Way's central supermassive black hole. We also consider what the next generation of ground- and space- based telescopes may uncover.
May 28, 2015 Brant Robertson - University of Arizona New Constraints on Cosmic Reionization from Planck and Hubble Space Telescope Understanding cosmic reionization requires the identification and characterization of early sources of hydrogen-ionizing photons. The 2012 Hubble Ultra Deep Field (UDF12) campaign acquired the deepest blank-field infrared images with the Wide Field Camera 3 aboard Hubble Space Telescope and, for the first time, systematically explored the galaxy population deep into the era when cosmic microwave background (CMB) data indicates reionization was underway. High-redshift observations with HST including UDF12, CANDELS, and the Frontier Fields provide the best constraints to date on the abundance, luminosity distribution, and spectral properties of early star-forming galaxies. We synthesize results from these HST campaigns and the most recent constraints from Planck CMB observations to infer redshift-dependent ultraviolet luminosity densities, reionization histories, and electron scattering optical depth evolution consistent with the available data. We review these results, and discuss future avenues for progress in understanding the epoch of reionization.
May 21, 2015 Heather Knutson - Caltech Atmospheres of Extrasolar Planets in the Super-Earth Era Ongoing surveys of nearby stars have revealed an amazing diversity of planetary systems, many of which have characteristics that differ substantially from those of the solar system planets. Perhaps one of the biggest surprises to come out of these surveys was the discovery that "super-Earths" (planets between 1-10 times the mass of the Earth) are in fact the most common type of extrasolar planet. Despite the name we actually know very little about the compositions of these mysterious planets, and it has been suggested that this mass range may include both "water worlds" and "mini-Neptunes" with thick hydrogen envelopes in addition to more Earth-like terrestrial planets. In my talk I will explore current constraints on the compositions of planets with masses ranging from that of Neptune down into the super-Earth regime, and discuss the corresponding implications for our understanding of planet formation and evolution.
May 14, 2015 Joel Primack - UCSC New Insights on Galaxy Formation from Comparisons of Simulated and Observed Galaxies Computer simulations and theoretical understanding have now reached a stage where simulations are increasingly able to tackle the complexity of galaxy formation and evolution. This talk will describe in particular the successes and challenges of high-resolution hydrodynamic galaxy simulations, now including radiative pressure feedback, in trying to understand the Hubble Space Telescope observations of galaxies during the period of most vigorous star formation (1 < z < 3, “Cosmic High Noon”) [1]. I used to think that galaxies form as disks, that forming galaxies are pretty smooth, and that galaxies generally grow in radius as they grow in mass — but we are now learning that all these statements are false. The majority of star-forming galaxies at z > 1 have recently been shown to have mostly elongated (prolate) stellar distributions [2] rather than disks or spheroids, and our simulations may explain why [3]. A large fraction of star-forming galaxies at redshifts 1 < z < 3 are found to have massive stellar clumps [4]; these originate from violent disk instabilities in our simulations [5-6], which also help to create compact spheroids (“nuggets”) through galaxy compaction [7-9]. We are trying to understand how angular momentum evolves as gas falls toward the inner galaxy and becomes stars [10]. The talk will also describe the Assembling Galaxies of Resolved Anatomy (AGORA) program to run high-resolution simulations using as much as possible the same initial conditions, physical assumptions, and output analysis procedures. AGORA will systematically compare galaxy simulations using a wide variety of computer codes with each other and with observations, and thus improve understanding of galaxy formation [11].
May 7, 2015 Zhiqiang Mao - Tulane University Interplay between magnetism and superconductivity in iron chalcogenide The interplay between magnetism and superconductivity in Fe-based superconductor systems is currently a subject of intense studies. The iron chalcogenide Fe1+y(Te1-xSex) is of particular interest due to its unique magnetic properties. While the parent compound Fe1+yTe shows antiferromagnetism with (p,0) in-plane magnetic wave vector, the optimally doped sample displays superconductivity with (p,p) spin resonance. This contrasts with iron pnictides in which both the parent compound’s antiferromagnetism and the doped samples’ superconducting (SC) spin resonance are characterized by the in-plane Fermi surface nesting wave vector Qn = (p,p). The evolution from (p,0) magnetism to superconductivity with (p,p) spin resonance in iron chalcogenides is associated with coexistence of magnetic correlations at (p,0) and (p,p). The other remarkable difference between iron chalcogenide and iron pnictide superconductors is their phase diagrams. In iron pnictides, bulk superconductivity either emerges immediately following suppression of long-range (p,p) antiferromagnetic (AFM) order, or coexists with it in a particular composition range. In contrast, in iron chalcogenides, bulk superconductivity does not appear immediately following the suppression of long-range (p,0) AFM order. Instead, an intermediate phase with weak charge carrier localization appears between AFM order and bulk superconductivity for 0.09 < x < 0.3. In this talk, I will first present an overview on the results summarized above and then introduce our recent studies on the coupling between electronic and magnetic properties in this system. I will show the doping dependences of Sommerfeld coefficient ?, Hall coefficient RH and Hall angle as well as their relations with superconductivity. The origin of superconductivity suppression and charge carrier localization in the underdoped region will be discussed in terms of these experimental results.
April 23, 2015 Alex Evilevitch - Carnegie Mellon University Physical Mechanisms of Viral Life-Cycle Herpesviruses are a leading cause of human viral disease, second only to influenza and cold viruses. Herpesviruses consist of a double-stranded (ds) DNA genome contained within a protein shell, termed the capsid, that is surrounded by an unstructured protein layer (the tegument) and a lipid-envelope. During viral replication, an ATP-dependent motor packages the genome into a preformed capsid through a unique opening created by the portal complex. Herpes Simplex virus type 1 (HSV-1) is a prototypical model system to study the general infection mechanisms of herpesviruses and other viruses that release their genome into the cell nucleus without capsid disassembly. We have recently shown that HSV-1 genome packaging creates an internal pressure of tens of atmospheres within the viral capsid. This pressure results from bending stress and repulsive forces acting on the tightly packaged DNA molecule. We also found that despite its liquid crystalline state inside the capsid, the DNA is fluid-like which facilitates its ejection into the cell nucleus during infection. The fluidity or, equivalently, mobility of the closely packaged DNA strands caused by interstrand repulsive interactions is regulated by the ionic environment of the cellular cytoplasm. Between rounds of replication, the virion must be sufficiently stable to ensure that the packaged genome is retained within the capsid. Conversely, during infection the virion must be unstable enough to allow genome release into the cell nucleus. A precise balance between these physical aspects of the viral capsid and its encapsidated genome is crucial to the viral replication cycle. Using HSV-1 as our primary model system, we investigate the roles of intracapsid DNA mobility and capsid stability for viral replication with respect to retention of the packaged genome inside the capsid and its subsequent ejection during infection. These studies provide new insights into the key mechanisms facilitating as well as inhibiting viral infectivity. This knowledge establishes a foundation for the design of novel mutation resistant drugs for herpesviruses.
April 16, 2015 Mark Neyrinck - JHU How the Cosmological Dark-Matter Sheet Stretches and Folds up to form Cosmic Structures Structures in the Universe like galaxies, and filaments and clusters of galaxies, are essential components of the arrangement of matter on large scales. They form in analogy to the origami folding of a sheet of dark matter. I will discuss some new results about how this sheet stretches and bunches together in different places. An "origami approximation" is a toy model showing the kinds of structures that form, and the spins that can arise within them. This should help in understanding spin alignments between galaxies, relevant to the weak-lensing systematic effect of intrinsic ellipticity alignments.
April 9, 2015 James Bullock - UCI Cosmology in the Local Universe The Milky Way and its local environment provide a number of important constraints in the nature of dark matter and galaxy formation on the smallest non-linear scales. In this talk I will review some recent developments and what these may be telling us about our current cosmological model.
April 2, 2015 Robert Allen - UCR Tropical Width Changes Through the 20th and 21st Centuries: The Role of the Pacific Decadal Oscillation, Anthropogenic Aerosols and Implications for the Southwest US. Observations show the tropical belt has widened over the past few decades, a phenomenon associated with poleward migration of subtropical dry zones and large-scale atmospheric circulation. In addition to greenhouse gases, studies have also associated tropical widening with stratospheric ozone loss and heterogeneous warming agents. Here, we investigate how tropical belt width will change through the 21st century in response to several climate forcing agents. Models that include aerosol indirect effects yield significantly larger Northern Hemisphere (NH) tropical widening than models that lack aerosol indirect effects, including a reversal of the projected NH tropical contraction under RCP4.5 to significant tropical widening. Additional simulations show that future reductions in anthropogenic aerosols drive NH tropical widening as large as, or larger than, greenhouse gases. Although aerosol indirect effects remain uncertain, we conclude that they are important drivers of 21st century climate change and that future efforts to reduce air pollution may have significant impacts on the width of the tropical belt.
March 12, 2015 Javad Shabani - California Nano Systems Institute, UCSB InAs heterostructures with superconducting contacts It has been recently realized that materials with strong spin orbit coupling can lead to novel states of matter such as topological insulators and superconductors. This exciting development might lead to a number of useful applications ranging from spintronics to quantum computing. In particular, theory predicts that narrow band gap semiconductors with strong spin-obit coupling are a suitable platform for the realization of Majorana zero-energy modes, predicted to obey exotic non-Abelian braiding statistics. In this talk, we demonstrate the first realization of gate-defined wires where one-dimensional confinement is created using electrostatic potentials, on large area InAs two-dimensional electron systems (2DESs). The electronic properties of the parent 2DES are fully characterized in the region that wires are formed. This allows us to quantitatively compare the effect of disorder in gate- and etched-defined wires. We show that this scheme together with epitaxial growth of superconducting thin film on InAs heterostructures could provide new prospective solutions for scalable and complex wire networks.
February 26, 2015 Victor Brar - Caltech Surface Plasmons and Impurity States in Graphene Graphene, an atomically thin sheet of carbon atoms, provides a unique platform to study quasiparticle interactions and to create optical metamaterials with novel properties. The 2D nature and linear band structure of graphene give rise to a semi-metal behavior, with tunable dielectric properties and a high electron mobility. In the DC regime, these properties allow graphene to display novel screening behavior in the presence of charged impurities, which I will show can be probed directly using scanning tunneling spectroscopy (STM). At optical (mid-IR) frequencies, the graphene dielectric function is strongly perturbed by the presence of collective excitations known as surface plasmon polaritons (SPPs), which are optical modes - supported by free carriers - that are bound to the graphene sheet. These modes show a number of remarkable properties, including a carrier density dependent dispersion relation, and wavelengths that are more than 100 times shorter than freespace. I will show how the surface plasmons in graphene can be harnessed to create infrared metasurfaces that have tunable optical properties. These materials will be shown to exhibit extreme light-matter interactions that can control the macroscopic absorption and emission properties of nanostructured dielectric stacks.
February 19, 2015 Frank Wuerthwein - UCSD The Quest for Dark Matter at the LHC - A Supersymmetric perspective from CMS After the discovery of the Higgs Boson in Run 1 of the LHC, the new “holy grail” of collider physics is to be able to produce and study dark matter in the laboratory. In this talk, we will address the following questions: - Why do we think dark matter exists ? - How do we find & understand Dark Matter at the Large Hadron Collider (LHC) ? - Where are we now with the search ? - Where are we going within the next 20 years?
January 29, 2015 Briaqn Keating - UCSD The Twisted Universe: The discovery of B-mode polarization The era of Cosmic Microwave Background B-mode polarization cosmology began in March 2014 with two landmark papers released within a week of each other. The BICEP2 telescope observed from the South Pole for three seasons (2010–2012) and released results showing an excess of B-modes in the degree angular scale range with >5 sigma significance. We find that this excess could not be explained by instrumental systematics and it was confirmed in cross-correlation with BICEP1 (at 100 and 150 GHz) and preliminary data from the Keck Array. The observed B-mode power spectrum was well-fit by a lensed-LCDM cosmological model with the addition of primordial tensor fluctuations. However, it is impossible to rule out foreground contamination and we are working alongside the Planck team to resolve this matter. I will discuss the BICEP2 experiment, observations, and data analysis. One week before the BICEP2 announcement, the POLARBEAR telescope (which observed from the Atacama Desert, Chile for one season 2012-2013) announced the first evidence for B-modes at sub-degree scales caused by gravitational lensing of the CMB’s E-modes by large scale structure at low-redshift. The combination of the BICEP2 and POLARBEAR results paves the way towards precision tests of inflation, foreground contamination as well as probes of other aspects of fundamental physics including measuring the number and masses of cosmological neutrinos.
January 15, 2015 Jun Ye - JILA, National Institute of Standards and Technology and U Colorado Making the world’s best atomic clock The relentless pursuit of spectroscopy resolution has been a key drive for many scientific and technological breakthroughs over the past century, including the invention of laser and the creation of ultracold matter. State-of-the-art lasers now maintain optical phase coherence over many seconds and provide this piercing resolution across the entire visible spectrum. The new capability in control of light has enabled us to create and probe novel quantum matter via manipulation of dilute atomic and molecular gases at ultralow temperatures. For the first time, we control the quantum states of more than 1000 atoms so precisely that we achieve a more stable and accurate atomic clock than any existing atomic clocks, with both key ingredients for a clock reaching the 10-18 level. We are also on the verge of integrating novel many-body quantum states into the frontiers of precision metrology, ready to advance measurement precision beyond the standard quantum limit. Such advanced clocks will allow us to test the fundamental laws of nature and find applications among a wide range of technological frontiers.
January 8, 2015 Kang Wang - UCLA Electrical Engineering Magnetization switching through giant spin-orbit torque in the magnetically doped topological insulators Recent demonstrations of magnetization switching induced by in-plane current in heavy metal/ferromagnetic heterostructures have drawn great interest to spin torques arising from the large spin-orbit coupling (SOC) [1-3]. Due to the intrinsic extraordinarily strong SOC and spin-momentum lock, topological insulators (TIs) are expected to be promising candidates for exploring spin-orbit torque (SOT)-related physics [4, 5]. In this talk, I will describe the properties of TI from quantum Hall to quantum anomalous Hall. The realization of quantum anomalous Hall as well as its robustness in nonlocal transport measurements will be discussed for magnetic doped TI grown by molecular beam epitaxy. I will then report the magnetization switching through giant SOT in the magnetically doped TI structures. In particular, we will show a magnetization switching in a chromium-doped magnetic TI bilayer heterostructure by current; this large current induced SOT may have significant contributions from the spin-momentum locked surface states of TI. The critical current density for switching is shown to be as low as below 8.9 × 104A/cm2 at 1.9 K. Moreover, a second-harmonic method is used to measure the spin torque efficiencies, which are more than three orders of magnitude larger than those reported in heavy metals. The giant SOT and efficient current-induced magnetization switching exhibited in the bilayer heterostructure may lead to innovative spintronics applications for ultralow power dissipation memory and logic devices.
December 11, 2014 Joan R. Najita - National Optical Astronomy Observatory Thanksgiving Tales of Planet Formation: Feast, Famine, or…? The large number and diversity of planetary systems discovered to date present new challenges for planet formation theory. Core accretion remains the dominant paradigm of planet formation, despite these challenges. Yet what evidence do we have that core accretion actually occurs? I will discuss observations of nearby protoplanetary disks that may address this question. I will also illustrate how a comparison of protoplanetary disk and exoplanet populations lends insights into the basic nature of the planet formation process, e.g., when it begins and whether it is "easy", "hard", or something else.
December 4, 2014 Paul M. Goldbart - Georgia Tech Description:Seeking simplicity in complexity: A physicist’s view of vulcanized media Vulcanized media – materials that acquire their valuable and unusual properties through the random chemical linking of their molecular constituents – surround us, from the tires of our cars to the tubing of wine-making and medicine, to rubber bands, flooring and waterproof clothing. The aim of this talk is to look at vulcanized media through the lens of condensed matter physics, and to ask how their properties – most notably their universal random structure and rigidity – emerge via of the collective behavior of their constituents. Along the way, we shall see that, provided some twists are added, a familiar field theory allows us to identify at least some simplicity in these archetypes of complexity
November 20, 2014 Steven A. Rodney - Johns Hopkins University The New Frontier : Type Ia Supernovae in the Early Universe The explosion of a white dwarf in a binary system produces a Type Ia Supernova (SN Ia). These are powerful tools for measuring cosmic distances, but we still lack a complete understanding of how these systems evolve to the point of explosion. With the CLASH and CANDELS programs on the Hubble Space Telescope we have pushed back the frontier of SN discovery, to an era when the universe was only ~3 Gyr old. I'll describe how we are using this unique high-z sample to test SN Ia progenitor models and to deliver unique constraints on dark energy. Finally, I'll share some challenging and perplexing preliminary results from the first year of the FrontierSN program: an HST search for supernovae behind strong-lensing galaxy clusters.
November 13, 2014 R. Shankar - Yale Hamiltonian Theory of Fractional Chern Bands It has been known for some time that a system with a filled band will have an integer quantum Hall conductance equal to its Chern number, a topological index associated with the band. While this is true for a system in a magnetic field with filled Landau Levels, even a system in zero external field can exhibit the quantum Hall effect (QHE) if its band has a Chern number. I review this issue and discuss a more recent question of whether a partially filled Chern band can exhibit the Fractional QHE. I describe the work done with Ganpathy Murthy in which we show how composite fermions, which were so useful in explaining the usual FQHE, can be introduced here and with equal success by adapting our Hamiltonian Theory of composite fermions developed for the FQHE in the continuum.
November 6, 2014 Vivek Aji -UC Riverside When spin meets momentum… Over the past decade a number of new phases and novel phenomena have been discovered in quantum many particle systems when the spin of the electron is strongly coupled to its momentum. In many instances these phases are topologically nontrivial. In this talk I discuss these developments using the Weyl semimetal as a canonical example. The system supports massless fermonic excitations in three dimensions, providing laboratory realizations of phenomena once studied in the context of neutrinos. I will provide a route to detecting their existence and address the question of what new phases of matter they support due to electron electron interactions. If time permits I will discuss promising new directions enabled by the presence of strong spin orbital coupling.
October 30, 2014 Massimo Vergassola -UCSD Navigating turbulent environments Insects signaling to potential mates and olfactory robots (sniffers) searching for chemical leaks raise similar challenging issues. Molecules emitted by a source are mixed in the turbulent environment, which breaks up regions of high concentration into random and disconnected patches. Searchers detect them intermittently as patches sweep by on the wind. We recently quantified the statistics of detections by experiments and statistical physics methods for the transport of Lagrangian particles in turbulent flow. I shall discuss these results and why the climbing of concentration gradients is ineffective for locating the source. A strategy of movement based on sparse and sporadic cues must be devised for long-distance olfactory searches. I shall then present some possibilities, their applications to sniffers as well as consequences for the neurobiology of insect olfactory searches.
October 23, 2014 Daniel Whiteson -UC Irvine Your smartphone is a cosmic-ray detector We propose a novel approach for observing cosmic rays at ultra-high energy (>1018 eV) by re-purposing the existing network of smartphones as a ground detector array. Extensive air showers generated by cosmic rays produce muons and high-energy photons, which can be detected by the CMOS sensors of smartphone cameras. The small size and low efficiency of each sensor is compensated by the large number of active phones. We show that if user adoption targets are met, such a network will have significant observing power at the highest energies.
October 16, 2014 Naveen Reddy -UC Riverside Description:The MOSFIRE Deep Evolution Field (MOSDEF) Survey: A Transformative Exploration of Distant Galaxies Rest-frame optical spectroscopy provides key insights into the star formation, dust obscuration, chemical and stellar contents, radiation field and gas properties, and dynamics of galaxies in the distant universe. Yet this information has been lacking for large samples of galaxies at redshifts 1.4
October 9, 2014 Erik Winfree -Caltech Molecular Machines, Self-Assembly, and Circuits Made of DNA Single-stranded and double-stranded DNA molecules of any chosen sequence can now be readily synthesized. This puts us in position to experimentally investigate what may seem like a fundamental question about DNA structure and dynamics: toss some DNA into a test tube, and what happens? Does the equilibrium consist of double-stranded DNA? Is equilibrium always achieved quickly? If not, what kinds of structures can form, and with what temporal dynamics? What general principles govern the behavior? Surprisingly, concepts from computer science and engineering provide illuminating (partial) answers. In this talk, I will describe advances in both structural and dynamic DNA nanotechnology, with an emphasis on how dynamic circuits can be constructed systematically using the principles of DNA hybridization and branch migration.
October 2, 2014 Wes Campbell -UCLA Simulation and spectroscopy of many-body systems with cold atoms and molecules A lattice of strongly-interacting quantum spins may be simulated effectively on a classical supercomputer so long as the number of spins N is smaller than about 20-50 (depending upon the interaction model). Past this point, the Hilbert space accessible to the system (which grows exponentially with N) requires too much memory to simulate, and we seek new methods to examine the crossover from the few-body to many-body regimes. A quantum simulator is a device that is in principle capable of simulating these systems in this regime because it has access to its own exponentially-large Hilbert space. I will describe work using a quantum simulator made from trapped atomic ions to simulate strongly-coupled quantum systems, and describe new methods for performing spectroscopy on the many-body system. I will also discuss progress toward implementing other quantum simulations with a collection of cold dipolar molecules.
June 5, 2014 Hari C. Manoharan -Stanford Emergent Topological Phases in Quantum Materials Assembled Atom-by-Atom The observation of massless Dirac fermions in monolayer graphene has propelled a new area of science and technology seeking to harness charge carriers that behave relativistically within solid-state materials. Using low-temperature scanning tunneling microscopy and spectroscopy, we show the emergence of Dirac fermions in a fully tunable condensed-matter system—molecular graphene—assembled via atomic manipulation of a conventional two-dimensional electron system in a surface state. We embed, image, and tune the symmetries underlying the two-dimensional Dirac equation into these electrons by sculpting the surface potential with manipulated molecules. By distorting the effective electron hopping parameters into a Kekulé pattern, we find that these natively massless Dirac particles can be endowed with a tunable mass engendered by the associated scalar gauge field, in analogy to the Higgs field. With altered symmetry and texturing of the assembled lattices, the Dirac fermions can be dressed with gauge electric or magnetic fields such that the carriers believe they are in real fields and condense into the corresponding ground state, as confirmed by tunneling spectroscopy. Using these techniques we ultimately fabricate a quantum Hall state without breaking time-reversal symmetry, in which electrons quantize in a gauge magnetic field ramped to 60 Tesla with zero applied laboratory field. We show that these and other chiral states now possible to realize have direct analogues in topological insulators, and can be used to guide or confine charge in nontrivial ways [1,2]. [1] K. K. Gomes, W. Mar, W. Ko, F. Guinea, H. C. Manoharan, “Designer Dirac Fermions and Topological Phases in Molecular Graphene,” Nature 483, 306–310 (2012). [2] M. Polini, F. Guinea, M. Lewenstein, H. C. Manoharan, V. Pellegrini, “Artificial Honeycomb Lattices for Electrons, Atoms, and Photons,” Nature Nanotechnology 8, 625–633 (2013).
May 29, 2014 Xingjiang Zhou -IOP Beijing Laser-Based ARPES on High Temperature Cuprate Superconductors The discovery of high temperature superconductivity in copper-oxide compounds in 1986 has challenged the conventional theories of condensed matter physics for nearly three decades. Angle-resolved photoemission spectroscopy (ARPES) has played a key role in understanding the electronic structure and superconductivity mechanism of the high-Tc cuprate superconductors. In this talk, I will first report on the latest development of vacuum ultra-violet (VUV) laser-based ARPES systems that have superior performance including super-high energy resolution, super-high photon flux and enhanced bulk sensitivity. Then I will focus on some recent progress we have made, by utilizing the VUV-laser based ARPES, in studying high temperature cuprate superconductors[1-5]. [1]. Wentao Zhang et al., Phys. Rev. Lett. 100 (2008) 107002; [2]. Wentao Zhang et al., Phys. Rev. Lett. 101 (2008) 017002; [3]. Jianqiao Meng et al., Nature, 462 (2009) 335; [4]. Junfeng He et al., Phys. Rev. Lett. 111 (2013) 107005; [5]. Yingying Peng et al., Nature Communications 4 (2013) 2459.
May 22, 2014 David Hsieh -Caltech Description:Laser-based surface spectroscopic studies of topological insulators Over the past several years, topological insulators have become an intensively researched topic in condensed matter physics. Interest in these materials stems not only from their being a fundamentally new phase of quantum matter, but also because they hold promise for novel technological applications ranging from low power spin-based electronics to fault-tolerant quantum computers. In this talk I will describe results from ultrafast laser-based techniques that we use to study the interaction between the topological electronic states of Bi2Se3 and light. These include time-of-flight spin- and angle-resolved photoemission spectroscopy, photo-induced electrical transport and time-resolved optical second harmonic generation. I will discuss how these techniques can be used to visualize detailed spin textures in topological insulators and to excite spin-polarized currents for potential spintronics applications.
May 15, 2014 Joseph Polchinski -KITP & UCSB Description:The Black Hole Information Paradox, Alive and Kicking Thought experiments have played an important role in figuring out the laws of physics. For the unification of quantum mechanics and gravity, where the phenomena take place in extreme regimes, they are even more crucial. Hawking's 1976 paper "Breakdown of Predictability in Gravitational Collapse" presented one of the great thought experiments in the history of physics, arguing that black holes destroy information in a way that requires a modification of the laws of quantum mechanics. Skeptics for years failed to poke holes in Hawking's argument, but concluded that if quantum mechanics is to be saved then our understanding of spacetime must break down in a radical way. For a time it seemed that Maldacena's discovery of gauge/gravity duality had resolved the issue, but the recent firewall argument has opened many new questions.
May 8, 2014 Alexander Kusenko -UCLA Cosmic connections: from cosmic rays to gamma rays, to cosmic backgrounds and magnetic fields Combined data from gamma-ray telescopes, cosmic-ray detectors, and neutrino detectors have produced some surprising new insights regarding the most powerful sources in the universe, as well as intergalactic and galactic magnetic fields and extragalactic background light. I will discuss how a unified treatment of gamma rays, cosmic rays, and neutrinos reveals some intriguing connections between several seemingly unrelated phenomena.
May 1, 2014 Gerald Gabrielse -Harvard Description:The Amazing Electron and Its Moments: Most Stringent Tests of the Standard Model and Proposed Extensions The standard model of particle physics is the great triumph and the great frustration of modern physics. It predicts the value of the electron magnetic moment -- the most precisely measured property of an elementary particle -- to better than a part per trillion. Yet, it cannot explain why a universe made of matter rather than antimatter remains after the big bang, or dark energy, or dark matter, or inflation. Our ACME collaboration has just completed a 12 times more sensitive measurement of the electron's electric dipole moment. Extensions to the standard model, posited to possibly fix some deficiencies of the standard model, generally predict an electron electric dipole moment that could be within range of this new measurement sensitivity. This is a good place to test such extensions to the standard model insofar as the standard model predicts that the electric dipole moment of the electron is much too small to measure.
April 24, 2014 Marcel Franz -UBC Ettore Majorana and his strange particles In 1937 Italian physicist Ettore Majorana predicted the existence of strange fermionic particles that are their own antiparticles. It is possible that neutrinos realize such Majorana fermions but 75 years after the historical prediction the evidence remains inconclusive. In this talk I will describe recent efforts to engineer and observe Majorana fermions in solid state systems which appear to be very close to fruition. Majorana fermions have been theoretically predicted to occur in a class of systems called topological superconductors. Although such systems do not seem to exist in nature they can be engineered by combining other ingredients such as the ordinary superconductors and semiconductors with strong spin-orbit coupling or topological insulators. Signatures consistent with Majorana fermions have already been reported in such hybrid devices and the race is on for the first conclusive experimental observation. I will explain the intriguing physics behind these solid-state realizations of Majorana fermions and discuss their significance for future technologies.
April 17, 2014 Leonid Levitov -MIT Atomic collapse in graphene Since the discovery that electrons in graphene behave as massless Dirac fermions, the single-atom-thick material has become a fertile playground for testing exotic predictions of quantum electrodynamics, such as Klein tunneling and the fractional quantum Hall effect. Now add to that list atomic collapse, the spontaneous formation of electrons and positrons in the electrostatic field of a superheavy atomic nucleus. The atomic collapse was predicted to manifest itself in quasistationary states which have complex-valued energies and which decay rapidly. However, the atoms created artificially in laboratory have nuclear charge only up to Z=118, which falls short of the predicted threshold for collapse, Interest in this problem has been revived with the advent of graphene, where because of a large fine structure constant the collapse is expected for Z of order unity. In this talk we will discuss the symmetry aspects of atomic collapse, in particular the anomalous breaking of scale invariance. We will also describe recent experiments that use scanning tunneling microscopy (STM) to probe atomic collapse near STM-controlled artificial compound nuclei.
April 10, 2014 Johnpierre Paglione -University of Maryland Description:Toward true topological insulator materials Bismuth selenide, regarded as the archetype topological insulator material, is in reality a good conducting metal with bulk carriers that derive from a self-doping caused by selenium vacancies. We report the synthesis of stoichiometric Bi2Se3 crystals that exhibit nonmetallic behavior in electrical transport down to low temperatures, providing the first indications of a truly insulating topological insulator material. I will discuss the peculiar presence of both electron- and hole-like carriers, along with the achievement of ambipolar transport in bulk Bi2Se3 crystals without gating techniques. In addition, new quantum transport studies of the proposed topological Kondo insulator samarium hexaboride will present our findings of a unique signature of non-trivial surface states.
April 3, 2014 Harry Ferguson - Space Telescope Science Institute Observing Galaxy Assembly The Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) is a multi-cycle observing program with the Hubble space telescope (and many other facilities) designed to document the first third of galactic evolution, from redshift z~8 to 1.5. It is also designed to find and measure Type Ia SNe beyond z > 1.5 and test their accuracy as standard candles for cosmology. The Hubble observations were completed in August 2013. The talk will discuss findings from ongoing analysis of the survey data, including properties of galaxies near cosmic reionization, and the evolution of star-forming and passive galaxies as the Hubble sequence begins to emerge a few billion years later.
March 13, 2014 Professor Simona Murgia -UC Irvine Description:Indirect detection of dark matter with gamma rays Evidence for dark matter is overwhelming. From experimental data we can infer that dark matter constitutes most of the matter in the Universe and that it interacts very weakly, and at least gravitationally, with ordinary matter. However we do not know what it is. Several theoretical models have been proposed that predict the existence of Weakly Interacting Massive Particles (WIMPs) that are excellent dark matter candidates. The existence of WIMPs can be tested indirectly, primarily through their annihilation or decay into photons. In this talk I'll present the latest results on these searches by Fermi LAT.
March 6, 2014 Professor Chang Kee Jung - Observation of Electron Neutrino Appearance from a Muon Neutrino Beam Matter-antimatter asymmetry is one of the most outstanding mysteries of the universe. The experimental observation of CP-violation (CPV) in the lepton sector could prove to be one of the most important discoveries in our understanding of the universe. In 2011, the T2K experiment published a result that indicates a non-zero theta_{13}, the last unknown mixing angle in the lepton sector at that time, at 2.5 sigma level of significance, which was the first evidence of non-zero \theta_{13} by a single experiement. Recently, after analyzing two more years of data, the experiment reported "Observation of electron neutrino appearance from a muon neutrino beam" at 7.5 sigma level of significance. While neutrino oscillation has been well-established since the discovery by the Super-Kamiokande experiment in 1998, there have not been a definitive observation of neutrino oscillation in a so-called "appearance mode", and this new T2K observation is the first time an explicit neutrino flavor (electron) appearance is observed from another neutrino flavor (muon). This observation also opens the door to study CPV in neutrinos. When incorporating recent precision measurements on theta_{13} by the reactor experiments, especially Daya Bay, along with other neutrino oscillation parameter measurements, T2K data show an intriguing initial result on delta_{CP}. In this talk I will present the details of this discovery and its importance to the future CPV measurements in the lepton sector, as well as other recent results.
February 27, 2014 Professor Giorgio Gratta -Stanford The EXO program and the quest for Majorana Neutrino Masses With the definitive evidence for neutrino oscillations collected in the last decade, we now believe that neutrino masses are non-zero. Oscillation measurements, however, only measure mass differences and give us little information about the absolute values of neutrino masses. The hypothetical phenomenon of neutrino-less double-beta decay can probe the neutrino mass scale with exquisite sensitivity. This process, if observed, would also imply that neutrinos, unlike all other spin-1/2 particles, are of the Majorana type, that is they have wave functions with only two compenents. The observation of the neutrino-less double-beta decay would also imply the non-conservation of the lepton number. Following the well known principle that there is no free lunch in life, interesting half-lives for neutrino-less double-beta decay exceed 10^25 years (or ~10^15 times the age of the Universe) making experiments rather challenging. I will describe the the EXO program, including the recent measurements by EXO-200 that establish the present state of the art and the plans for a 5-ton enriched Xe detector, nEXO, that will have a sensitivity to Majorana masses below 10meV.
February 20, 2014 Professor David Shih -Rutgers The Search for Supersymmetry at the LHC The LHC discovery of the Higgs boson in 2012 was a stunning success for the Standard Model of particle physics. However, at the same time, the discovery of the Higgs also reinforced the urgency of the "hierarchy problem" -- how did the Higgs (and the rest of the Standard Model) end up so much lighter than the Planck scale? In this talk, I will give a non-technical overview of supersymmetry, one of the most popular and promising solutions to the hierarchy problem. I will describe the basic framework of supersymmetry, its major successes and predictions, and the current status of searches for it at the LHC.
February 6, 2014 Dr. Jean-Pierre Delahaye -SLAC Lepton colliders in the multi-TeV energy range In preparation for a Lepton Collider in the multi-TeV range which will possibly be required for precision physics beyond the standard model if and when identified, novel acceleration techniques are being developed with attractive performances. After a review of the schemes being considered for an affordable e+/- linear collider at the energy frontier, the presentation will focus on Muon-based facilities which offer a unique potential to provide capabilities at both the Intensity Frontier with Neutrino Factories and the Energy Frontier with Muon Colliders ranging from Higgs to multi-TeV energies. They rely on novel technology with challenging parameters, from which the feasibility is currently being assessed by the U.S. Muon Accelerator Program (MAP). A realistic scenario for a complementary series of staged facilities with increasing complexity and significant physics potential at each stage has been developed. The rationale and sequence of the staging process, as well as the critical issues to be addressed at each stage, are presented.
January 30, 2014 Professor Jonathan Feng - UC Irvine Dark matter and the LHC Dark matter makes up a quarter of the Universe, but it cannot be any of the known particles. Dark matter is now arguably the leading motivation to look for new particles, and this search has gone into high gear with spectacular progress in dedicated searches, as well as the start of the LHC. I will describe the interplay of dark matter searches and particle colliders, the current status and upcoming prospects, as well as some more speculative ideas of what the future may bring.
January 23, 2014 Dr. Alan Drew -Queen Mary University of London Local probe investigation of spin and charge dynamics in organic semiconductors Organic semiconductors fall into a class of materials that shows significant potential for future applications and as a result, the field is becoming extremely topical. This is due to their ease of processing, low cost, highly tuneable electronic properties, favourable mechanical properties and long spin coherence times. The latter point makes them extremely promising for future spintronic applications. However, there is a lack of suitable techniques that can yield information on intrinsic spin and charge carrier dynamics in organic materials. For example, many of the experimental techniques available that probe the spin polarisation of charge carriers in inorganic spintronic devices/materials are not always applicable to organic materials. Muon spectroscopy is a technique that has rarely been applied to study spintronic problems in inorganic systems, yet is ideally suited to studying them in organic semiconductors. Therefore, I will discuss a number of recent results that involve using muon’s as a probe of spin transport and dynamics in organic semiconductors.
January 16, 2014 Professor Sunil Golwala -Caltech Paradigm Shifts and Innovation in the Search for Dark Matter For almost 30 years, the Weakly Interacting Massive Particle (WIMP) has been the favored candidate for the dark matter, with its motivation strengthening as supersymmetry became the favored theory for physics beyond the Standard Model. However, the past few years have seen a paradigm shift toward a broader set of models for dark matter, driven by both experimental results and theoretical work, and we now have a broader view of what dark matter might be. This shift in our paradigm for dark matter has encouraged experimental innovation, motivating efforts the extend the reach of current technologies to lower WIMP masses and encouraging the direct detection community to develop an exhaustive experimental strategy for detecting and understanding the dark matter. I will review the status of current searches for WIMP and WIMP-like dark matter, using recent results from the SuperCDMS Soudan experiment as an example of the experimental response to these changes, and present some scenarios for how the field might evolve.
January 9, 2014 Professor Michael Peskin -SLAC, Stanford University Beyond the Higgs Boson: Further questions and expectations for the Large Hadron Collider The biggest recent news from particle physics is the discovery at the CERN Large Hadron Collider of a new particle with many properties of the long-sought Higgs Boson. The Higgs Boson had been predicted by the unified theory of weak and electromagnetic interactions. This discovery thus seems to fill a recognized gap in our understanding. But there are more mysteries about the weak interactions and physics at the 100 GeV - 1 TeV mass scale. About these, the LHC has also given us much information, but all of it negative, exclusions of previously possible solutions. In this lecture, I will give my best understanding of where we are in the search for new particles and forces related to the weak interactions. I will review the questions we are asking about physics in the hundred GeV region. I will discuss the power and also the difficulties of LHC measurements. There are many alternatives for the route forward. I will discuss some of these and their implications for the future program of physics at high-energy colliders.
December 5, 2013 Massimo Stiavelli - Space Telescope Science Institute James Webb Space Telescope (JWST): Reionization and First Light I will discuss what existing data tell us about the reionization of the Universe and the role played by faint galaxies including some new results derived by constraining the faint end of the luminosity function at redshift 6 using a form of surface brightness fluctuations analysis. I will also discuss expectations for the JWST contribution in this field. Moving to higher redshift I will discuss how JWST will study the first galaxies and the constraints it could place on the first stars by studying their supernovae.
November 21, 2013 Harold Y. Hwang - Stanford Emergent Phenomena at Oxide Interfaces Complex oxides are fascinating systems which host a vast array of unique phenomena, such as high temperature (and unconventional) superconductivity, ‘colossal’ magnetoresistance, all forms of magnetism and ferroelectricity, as well as (quantum) phase transitions and couplings between these states. In recent years, there has been a mini-revolution in our ability to grow thin film heterostructures of these materials with atomic precision. With this level of control, a number of new electronic phases have been discovered at their interfaces. Between two insulators, for example, metallic, superconducting, and magnetic states can be induced. In analogy to the rich science and technology that emerged from the development of semiconductor heterostructures, we are using these techniques to create novel low-dimensional states inaccessible in bulk oxides. After a general overview, I will focus on recent results on two-dimensional superconductivity in oxide heterostructures, contrasting two systems based on SrTiO3 which approach the ‘dirty’ and ‘clean’ limit.
November 14, 2013 Sean Hartnoll -Stanford) Ohm's law and black holes Over the past decade it has been understood that the dynamics of certain black holes, as probed by a distant observer, is indistinguishable from that of a strongly correlated dissipative medium. This correspondence offers to provide insights into long standing conceptual problems in unconventional metals. I will discuss the picture of charge transport (that is, Ohm's law) in strongly correlated media that has emerged from black hole physics.
November 7, 2013 David Reznick - UCR, Dept. of Biology Description:The Fast Pace of Evolution A traditional perspective of evolution is that it has played a vital role in shaping biological diversity, but that it is too slow to be observable in real time or to be amenable to experimental studies done in natural populations. For the first half of my seminar, I will outline how and why I performed this research and how it fits into our general understanding of evolution. Here I will show how predation has shaped the evolution of guppy life histories, which are the aggregate of traits that determine how organisms propagate. The components of the life history include the age at maturity, frequency of reproduction, proportional allocation of available resources to reproduction, and the number and size of offspring that are produced. This work was facilitated by there being natural variation among populations of guppies in their exposure to predators so that nature first did the experiment for me. Nature also created a template in which I could do the experiment myself by treating whole streams as if they were giant test tubes. In the second half of my seminar I will present some highlights of my current research program, which is devoted to the study of the way ecology and evolution interact in natural ecosystems. The traditional perspective for this relationship is that the environment defines a template and evolution by natural selection shapes the organism to fit that template. An alternative perspective is that ecology and evolution are interacting processes that can reciprocally shape one another. This alternative is well supported by a small body of theory and experiments in model laboratory ecosystems, but less well with research done in natural ecosystems. I and my colleagues are evaluating this proposition as part of a multidisciplinary, experimental study of evolution in natural populations of guppies.
October 24, 2013 Tom Murphy -UCSD Testing Gravity via Lunar Laser Ranging Forty years ago, Apollo astronauts placed the first of several retroreflector arrays on the Moon. Laser range measurements between the Earth and the Moon have provided some of our best tests to date of general relativity and gravitational phenomenology - including the equivalence principle, the time-rate-of-change of the gravitational constant, the inverse square law, and gravito-magnetism. A new effort called APOLLO (the Apache Point Observatory Lunar Laser-ranging Operation) is now collecting measurements at the unprecedented precision of one millimeter, which will produce order-of-magnitude improvements in a variety of gravitational tests, as well as reveal more detail about the interior structure of the Moon. This talk will include an overview of the science, a description of the instrument and its performance, evidence for dust accumulation on the lunar surface, re-discovery of a lost Soviet reflector, and an outlook for advancing the state of gravity tests in the solar system.
October 17, 2013 Nigel Hughes -UCR, Earth Sciences Constraining the uplift history of the Himalaya using fossil trilobites The Himalaya is the world's greatest mountain chain, but knowledge of its geological history remains incomplete. In particular, present knowledge of when movement occurred on the major fault systems fails to explain a major shift in ocean water chemistry that many have supposed tied to Himalayan erosional history. We have approached by seeking to reconstruct the form of the Himalayan margin prior to the collision of India with Asia. This is critical, because in order to know what has been eroded, we need to know what was originally present and when. By reconstructing the geological history of the Cambrian Period we can estimate the amount of material eroded from the Himalaya, and use this to reconcile the timing offset between Himalayan uplift and changing ocean chemistry.
October 10, 2013 David Jewitt -UCLA Comets and the Origin and Evolution of the Solar System Scientific interest in the comets lies in their role as the most primitive bodies in the solar system. They are also some of the most spectacular objects in the sky. Comets probe both the formation epoch and evolutionary processes occurring since the formation of the solar system. I will first provide a big-picture overview of the field and then discuss ongoing investigations into the major comet reservoirs, including a surprising new population discovered in the last decade.
October 3, 2013 Warren Skidmore -Thirty Metter Telescope Corporation, Pasadena Thirty Meter Telescope: The Next Generation of Ground Based Optical/Infra-Red Observatory I will discuss the scientific capabilities that the Thirty Meter Telescope will provide and some of the areas of study that will be revolutionized with the TMT. I'll describe how the telescope design was developed to support a broad range of observing capabilities and how the observatory is being engineered. Finally I'll describe the avenues through which individuals can actively participate in the project.
June 6, 2013 Dr. Brendan Crill -Jet Propulsion Laboratory Planck and the Universe: Fundamental Physics with Observations of the Cosmic Microwave Background Planck is the third-generation satellite aimed at measuring the cosmic microwave background, a relic of the hot big bang. Launched in May 2009 Planck has surveyed the full sky at high sensitivity, high angular Resolution, and with a broad range of frequencies from 30 to 857 GHz. This broad frequency coverage gives Planck a unique view of the history of the universe from the epoch of recombination (over 13 billion years ago) to the present. In this talk I will present Planck's sky maps and explain how we use them to reach conclusionsabout fundamental physics using the standard cosmological model and extensions to this model.
May 30, 2013 Prof. Gordon Watts - University of Washington The Higgs and its Impact on Particle Physics The recent discovery of a Higgs-like particle has gotten a great deal of attention in by both the public and the scientific community. I’ll discuss the results and updates since the discovery and touch briefly on how this discovery is steadily altering our view of particle physics and what questions need to be next addressed.
May 16, 2013 Dr. Starnes Walker -U.S. Fleet Cyber Command & U.S. 10th Fleet, U.S. Navy A Historical Journey of Physics Inspiration to Naval Research: A Pathway to Discovery and Innovation From the early 1900s physics contributions have created a foundational understanding of phenomenon playing a significant role in naval research. This understanding has led to discoveries and innovation allowing exploration and operations from the deepest ocean depths to far space. With the ability to explore these extreme environments, physics research spanning interdisciplinary fields continues to provide a lead role in defense science important to the nation’s security. A historical review of these contributions will be presented through the optics of strategic research initiatives at the Office of Naval Research and the Naval Research Laboratory.
May 9, 2013 Prof. Manuel Calderón de la Barca Sánchez - UC Davis The quest for beauty in Heavy Ion collisions We can study strongly interacting matter by colliding heavy ions, and the quarks and gluons they carry, at the highest possible energies. Simulations of Quantum Chromodynamics predict that a new state of matter exists at high temperature, known as the Quark-Gluon Plasma, where the color fields are not confined inside nucleons. One way to probe this high-temperature deconfinement effects is via the measurements of heavy quark bound states. In particular, b-quark bound states, commonly called bottomonia, are expected to be modified in a hot Quark-Gluon Plasma. Experimentally, the Upsilon mesons are the members of the bottomonium family that are most readily accessible. I will review the key ideas driving us to measure Upsilons in heavy ion collisions, and discuss the recent results of this research from RHIC and LHC experiments.
April 25, 2013 Ian Speilman -U. of Maryland / NIST Gauge fields with cold atoms Gauge fields are ubiquitous in Physics. For example, in the context of high energy physics, they are the fundamental carrier of forces; while in condensed matter systems the associated physical fields (electrical and magnetic) are essential in creating and understanding many-body phenomena. Here I present our experimental work synthesizing static gauge fields for ultracold neutral atoms (bosonic and fermionic alkali atoms), analogous to applied fields in condensed matter systems. I will discuss these static gauge fields in the language of spin-orbit coupling where it consists of an equal sum of Rashba and Dresselhaus couplings. In experiment, we couple two internal states of our alkali atoms with a pair of Raman'' lasers and load our degenerate quantum gas into the resulting adiabatic eigenstates. For a Bose gas, a function of the Raman laser strength, a new exchange-driven interaction between the two dressed spins develops, which drives a (quantum) phase transition from a state where the two dressed spin states spatially mix, to one where they phase separate. Going beyond this simple modification to the spin-dependent interaction, we show that in the limit of large laser intensity, the particles act as free atoms, but interact with contributions from higher even partial waves.
April 18, 2013 Sean Caroll -Caltech Making Sense of the Many Worlds Interpretation Many decades after it became established as the basis for how we think about the world, quantum mechanics remains a mysterious theory. One of the most provocative versions of the theory is the Many-Worlds Interpretation, due to Hugh Everett. The postulates of the theory are amazingly simple, but the implications are hard to swallow. One of the specific obstacles to accepting the Everett approach has been the status of the Born Rule -- the probability of an outcome is given by the wave function squared. I will discuss a new physics-based derivation of the Born Rule, as well as cosmological implications of the Many-Worlds Interpretation.
April 11, 2013 Fernando Martínez-Vidal -Univ. of Valencia Observation of time-reversal violation in B meson transitions In the standard model of elementary particle physics, charge-parity (CP) violation in the quark sector of weak interactions arises from the single physical phase of the three-generation Cabibbo-Kobayashi-Maskawa matrix. This mechanism has been validated by more than a decade of intense experimental work probing CP violation, particularly with the studies with B mesons at B factories, BABAR at SLAC (USA) and Belle at KEK (Japan). The success of the three-generation theory was recognized by the award of a share of the 2008 Nobel Prize in Physics to Kobayashi and Maskawa. Since the standard model is CPT invariant, it predicts a time-reversal (T) symmetry breaking matching the large observed CP asymmetry in B mesons. However, until recently, there has been no direct experimental observation of the expected, large T asymmetry. In this colloquium we shall first review the role of time symmetries in the laws of physics and the difficulties the experiments, using either stable or transition systems, have to afford to study directly fundamental time-reversal violation. In the second part we shall discuss how the decays of entangled neutral B mesons produced at B factories allow comparisons between the rates of four different transitions between quantum states and their inverse, as a function of the time evolution of the B meson. This technique, used by the BABAR experiment at the SLAC National Accelerator Laboratory, has lead to the first time-dependent, direct observation with high significance of T violation in transitions that can solely be related by a T symmetry transformation.
April 4, 2013 Roland Kawakami -UC Riverside UC Riverside Graphene has emerged as one of the most exciting systems for investigating spin transport and other spin-dependent phenomena. It turns out to be one of the best materials for spin transport, with room temperature spin diffusion lengths of several microns. This is far better than any other material. As a 2D atomic crystal, it turns out to be very surface sensitive and its spin-dependent properties could be modified by surface modifications. We are exploring induced phenomena such as magnetism in adatom-doped graphene as well as hybrid structures with complex oxides. Finally, I will discuss some concrete possibilities for technologies related to spin-based logic in graphene.
February 28, 2013 Hai-Bo Yu -University of Michigan Hunting for Dark Matter From Colliders to the Cosmos Astrophysical and cosmological observations provide compelling evidence for the existence of dark matter in the Universe, but its particle physics nature remains mysterious. The weakly-interacting massive particle (WIMP) has been proposed as a dark matter candidate. In this talk, I will first show that particle colliders like the Tevatron and the LHC are powerful tools to hunt for WIMP dark matter. I will also discuss dark matter models beyond the WIMP paradigm and search strategies for them. Astrophysical objects such as neutron stars, the Bullet Cluster, dwarf galaxies provide natural laboratories for exploring dark matter beyond the WIMP model.
February 21, 2013 Mark Wyman -University of Chicago A Sinister Universe- Gauge Fields, Inflation and Chiral Gravitational Waves Thirty years after its conception, inflation is now the cornerstone of today's cosmological standard model. However, connecting inflation to high energy physics has proved challenging. In this colloquium, I will outline a new direction in inflationary studies. The usual picture of a flat scalar field potential is replaced with an interacting system of scalar and gauge fields. The resulting class of models rely on the phenomenon of magnetic drift to extend inflation instead of Hubble friction. This mechanism is more robust to quantum corrections than scalar interactions alone. Additionally, such models have exciting new observational predictions, such as a parity-violating chiral spectrum of gravitational waves.
February 14, 2013 Timothy Lyons -Geosciences, UC Riverside The Early Rise of Oxygen in the Ocean and Atmosphere In the face of growing uncertainty about Archean organic biomarkers, our inorganic geochemical data provide the oldest and most compelling evidence for accumulation of oxygen in the atmosphere long before the so-called ‘Great Oxidation Event’ (GOE) roughly 2.4 billion years ago. Our data suggest that oxygen was very high in the wake of the GOE. Equally tantalizing is the indication of a precipitous drop in oxygen following this rise, which favored a return to an iron-rich, oxygen-poor ocean. At this point, oxygen likely remained very low in the atmosphere for most of a billion years, perhaps less than 0.1% of that present today. The deep ocean was dominantly anoxic (depleted of oxygen) and iron-rich in response, while euxinia (sulfide rich) was largely limited to productive margins and restricted marginal basins. Our recent work allows us to constrain, for the first time, ocean anoxia at 30-40% of the seafloor for large intervals of the mid-Proterozoic. Euxinia, limited to only ~1-10% of the seafloor, was enough to pull the concentrations of some metals below those favored by prokaryotes and eukaryotes, which likely throttled production and diversification. We know surprisingly little about the redox structure of the late Proterozoic ocean and atmosphere, but our studies point to oxygenation in the deepest waters. We propose that nutrient inputs linked to the end of Marinoan snowball Earth glaciation triggered the organic productivity/burial that spawned the rise in oxygen in the early Ediacaran. A logical implication is that atmospheric oxygen during the preceding mid-Proterozoic must have been very low to explain the apparent lack of animals. The past decade has witnessed a great revival in Precambrian studies, and our work has played a central role in defining the comprehensive landscape of ocean redox and the attendant network of feedbacks, including those tied to the co-evolution of life.
February 7, 2013 Kin Chung Fong -Caltech Listening to Graphene Noise: Progress Towards Microwave Photon Counter Graphene is a material with remarkable electronic properties. However its electronic thermodynamic properties are less explored. By listening to the noise from this atomically thin material sensitively, we can study the interesting thermal physics of the two-dimensional Dirac Fermions in graphene at low temperature. Our measurements suggest that graphene-based devices can generate substantial advances in the areas of ultra-sensitive bolometry, calorimetry, and microwave single photo-detection for applications in areas such as observational astronomy, quantum information and measurement.
January 24, 2013 Richard S. Ellis -Caltech Observations of Star-Forming Galaxies During the Reionization Era In this talk I present results from the deepest observations recently made by the Hubble Space Telescope (Hubble Ultra Deep Field-2012: HUDF12). The main aim of this study is to identify the first generation of galaxies at the dawn of time, when the Universe was less than 1 Billion years old. These galaxies are highly star-forming systems, rapidly building up their mass through star formation activity. A fraction of the photons generated through the star formation process will escape from this galaxy to the Inter-Galactic Medium (IGM). These are responsible for ionizing the neutral Hydrogen in the IGM. This process, so-called re-ionization, is responsible for the universe becoming transparent after the “dark ages”. I present the discovery of some of the highest redshift (most distant) galaxy candidates, their star formation activity and their role in the re-ionization process.
January 17, 2013 Brian Siana -UC Riverside Ultra-faint Galaxies and the Reionization of the Universe A primary goal of observational cosmology is to measure and understand the history of the star formation rate density of the universe. Over the past decade, astronomers have pushed these studies to larger look-back times to when the universe was only a few percent of its current age. It has become clear that at early epochs there is likely a large population of extremely faint galaxies beyond the detection limits of our deepest images. The presence of these galaxies is required to explain a number of phenomena - including the reionization of the hydrogen in the intergalactic medium - and yet we know little about them. I will discuss our efforts with the Hubble and Keck telescopes to find these ultra-faint galaxies and determine whether or not they caused the reionization of the universe.
January 17, 2013 Brian Siana - UC Riverside Search for low-MET supersymmetry at CMS Description:Supersymmetry (SUSY) garners much interest because it can simultaneously solve the hierarchy problem, allow unification of the fundamental interactions, and provide a candidate for dark matter. Most searches for SUSY focus on the presence of large missing transverse energy (MET) carried away by the lightest SUSY particle (LSP). As the parameter space available for high-MET SUSY is reduced by recent results from the CERN LHC, it becomes more important to study well motivated low-MET alternatives including models characterized by hidden sectors and R-parity violation (RPV). Though couplings are constrained by precision measurements of low energy processes, there is room for SUSY models with RPV, which allow decay of the LSP resulting in low-MET signatures. Additionally, the more recent "stealth" SUSY model yields low-MET signatures while conserving R-parity by means of a new hidden sector in which SUSY is approximately conserved. We present searches for low-MET SUSY in pp collisions at sqrt(s) = 7 TeV corresponding to 5/fb of integrated luminosity collected with the CMS detector in 2011. We search for stealth SUSY in events with two photons and several hadronic jets, and we search for RPV decays of a light top squark in events with two tau mesons and two b-tagged jets. Based on good agreement between the data and the standard model expectation, we determine limits on squark production in the framework of stealth SUSY and top squark production in the framework of RPV SUSY.
December 6, 2012 Steven Kivelson - Stanford Concerning Mott Insulating Phases “Band insulators” arise as a consequence of subtle quantum interference effects involving the multiple-scattering of electrons from the periodic crystalline lattice – electron-electron interactions are not fundamental to their existence. “Mott insulators” arise as a consequence of the strong repulsive interactions between electrons which, under appropriate circumstances, produce insulating behavior in a classical fashion analogous to traffic gridlock in an overpopulated city – one electron cannot move until the next one gets out of its way. As two different limiting behaviors, there is a clear distinction between these two situations, but in a fully quantum mechanical description of interacting electrons a debate has raged since before I was born concerning whether or not these terms designate distinct states of matter, and if so, how to distinguish them. In the last decade, as a theoretical point of principle, it has been established that distinct Mott insulating phases of matter exist, among which are some remarkable quantum phases with extraordinary properties such as electron fractionalization and topological order. I will discuss some of these developments, mostly as abstract theoretical issues, although in the end I will briefly discuss our attempts to provide a theoretical understanding of the currently most promising candidate insulating material - EtMe3Sb[Pd(dmit)2]2 - in which a number of spectacular experimental anomalies, including an infinite violation of the Wiedemann-Franz law, are suggestive of a particularly unusual “spin-liquid” ground-state phase. (Don’t worry if you don’t know what EtMe3Sb[Pd(dmit)2]2 stands for – I don’t know, either.)
November 29, 2012 Raissa D'Souza - UC Davis Percolating, Cascades, and Optimal Interdendence of Networks Collections of networks are at the core of modern society, spanning technological, biological and social systems. Over the past decade a science of networks has been emerging and providing insights into the structure and function of many diverse types of systems, such as protein-interactions in a cell, collaboration networks of scientists, and the World Wide Web. Statistical physics provides a framework for modeling network phenomena, especially phase transitions, such as the sudden emergence of large-scale connectivity. This talk will give an overview and present a variant of the classic Erdos-Renyi model of network formation, showing that we can alter the location and also the nature of the phase transition, making for an explosive onset of connectivity. We also develop random graph models of interacting networks, motivated by the fact that individual networks are increasingly interdependent (e.g., the Internet and the power grid, globalization of financial markets). We show that interactions between different types of networks can actually lower critical thresholds and provide stabilizing effects with respect to cascades.
November 15, 2012 Nigel Goldenfield - U Illinois, Urbana-Champaign Statistical Mechanics of the Genetic Code: A Glimpse of Early Life? Relics of early life, preceding even the last universal common ancestor of all life on Earth, are present in the structure of the modern day canonical genetic code --- the map between DNA sequence and amino acids that form proteins. The code is not random, as often assumed, but instead is now known to have certain error minimisation properties. How could such a code evolve, when it would seem that mutations to the code itself would cause the wrong proteins to be translated, thus killing the organism? Using digital life simulations, I show how a unique and optimal genetic code can emerge over evolutionary time, but only if horizontal gene transfer — a network effect — was a much stronger characteristic of early life than it is now. These results suggest a natural scenario in which evolution exhibits three distinct dynamical regimes, differentiated respectively by the way in which information flow, genetic novelty and complexity emerge. Possible observational signatures of these predictions are discussed.
November 8, 2012 Andrew Cohen - Boston University Electroweak Superconductivity Although the Standard Model of particle physics is many decades old, one of its most prominent features, electroweak superconductivity, remains poorly understood. I will give a gentle introduction to the subject and describe why we have been unsuccessful at fully understanding the origin of this phenomenon, the best ideas we have had to date, and why we might be on the verge of resolving this mystery.
November 1, 2012 James P. Eisenstein - Caltech Exciton Transport and Perfect Coulomb Drag A key attribute of typical quantum Hall systems is that they are topological insulators: They are electrical insulators in the bulk even though perfectly conducting chiral edge states lie at their boundaries. Most quantum Hall effect (QHE) experiments employ a simply-connected Hall bar geometry in which all current and voltage contacts lie at the sample’s boundary and are thus connected to these edge states. Such a geometry is sufficient for observing the vanishing longitudinal and quantized Hall resistances which are the hallmarks of the QHE. In contrast, multiply-connected geometries, such as a Corbino annulus with contacts on the inner and outer boundaries, provide clear demonstrations that the bulk of the 2D system is indeed insulating. In this talk I will discuss how a certain bilayer quantized Hall state modifies this scenario. Specifically, I will report the results of recent experiments in Corbino devices which clearly demonstrate that while the bulk of the bilayer quantized Hall phase at total Landau level filling factor n = 1 is an electrical insulator just like any other quantized Hall system, it is nonetheless possible to transport energy across it. I will show that this energy transport is enabled by the flow of charge neutral excitons across the bulk, with their emission and absorption at the edges taking place via Andreev reflection. In a closely related ongoing experiment, we have shown that a current flowing in one 2D layer can induce an equal, but oppositely directed, current in the other 2D layer even though there is no electrical connection between them.
October 18, 2012 Tommaso Treu - UCSB Cosmology from Gravitational Time Delays What is the universe made of? What is the origin of cosmic acceleration? Strong gravitational lenses where the background source is variable in time and the foreground deflector is a massive galaxy can be used very effectively as cosmic "standard rods" to measure the geometry and content on the universe and help answer those questions. Gravitational time delays constrain primarily the Hubble Constant and - in combination with other techniques - the equation of state of dark energy, flatness of the universe, and neutrino masses. I will illustrate recent advances in modelling techniques and data quality that enable a 7% measurement of the Hubble Constant from a single gravitational lens as well as constraints on the equation of state of dark energy and flatness comparable to those obtained with the best probes. A measurement of the Hubble Constant with absolute precision of <4% is in progress. I will show the first results and their implications. I will conclude by discussing the bright prospects of gravitational time delays as cosmographic probe.
October 11, 2012 Miguel Angel Aragon Calvo - John Hopkins University
October 4, 2012 Gail Hanson - UC Riverside What will we discover first at the Large Hadron Collider? The Higgs boson! The Large Hadron Collider (LHC) at CERN, the world’s largest and highest-energy particle accelerator, has made its first major discovery. A new boson has been observed with properties consistent with the Higgs boson, which was proposed nearly 50 years ago to give mass to the weak gauge bosons of the electroweak theory. Results will be presented from searches for the standard model Higgs boson at the LHC. Physicists from UCR are part of a large team of physicists who built the Compact Muon Solenoid (CMS), one of the four huge LHC experiments, and participated in the discovery.
June 7, 2012 Alexander Turbiner - Nuclear Science Institute UNAM, Mexico Atomic-Molecular Physics in a Strong Magnetic Field and Atmosphere of a Neutron Star
May 31, 2012 Chandra Varma - UCR Discovery of Higgs Bosons
May 24, 2012 Geoff Marcy - Berkeley ExoPlanets: From Jupiters to Earths New observations reveal the properties of exoplanets, from Jupiter-size to Earth-size. Observations give the distribution of planet sizes, their orbital distances, and their occurrence rate around stars of different types. Over 300 multiple-planet systems have recently been discovered, offering information on the structure and gravitational interactions within planetary systems. The Kepler space telescope is now detecting planets as small as Earth, and smaller. The detection of habitable planets having temperatures suitable for biology, 0-100C, is in reach.
May 17, 2012 Christoph A. Haselwandter - USC Structure of Elastic Membrane Deformations The biological function of membrane proteins is determined by a complex interplay between protein structure and the properties of the surrounding lipid bilayer. In particular, the bilayer hydrophobic core couples to the hydrophobic regions of membrane proteins, yielding membrane deformations which can be described quantitatively by the elasticity theory of membranes. Employing mechanosensitive ion channels as a model system we show that, in addition to the hydrophobic mismatch between membrane proteins and the surrounding lipid bilayer, the symmetry and shape of the hydrophobic surfaces of membrane proteins play an important role in the regulation of protein function by bilayer membranes. Moreover, we find that, for a given protein shape, the sign and strength of elastic interactions, and associated cooperative function of membrane proteins, can depend on the relative protein orientation. The approach developed here represents a first step towards a physical theory of how elastic interactions affect the molecular structure and biological function of proteins in the crowded membrane environment provided by living cells.
May 10, 2012 Lee Armus - Caltech GOALS and the High-Redshift Universe Revealed by Herschel Luminous Infrared Galaxies (LIRGs) are a mixture of single galaxies, disk galaxy pairs and advanced mergers, exhibiting enhanced star formation rates and a higher fraction of Active Galactic Nuclei (AGN) compared to less luminous galaxies. A detailed study of low-redshift LIRGs is critical for our understanding of the cosmic evolution of galaxies and black holes. With the Great Observatories All-sky LIRG Survey (GOALS), we are measuring the properties of a large, complete sample of low-redshift LIRGs across the electromagnetic spectrum. In this talk, I will focus on a few key results from our ongoing program that are helping us understand some surprising new results from studies of the high-redshift Universe with the Herschel Space Observatory, and look toward some upcoming studies that will be important for understanding how starbursts and AGN evolve and influence each other in dusty galaxies today.
May 3, 2012 Jim De Yoreo - Lawrence Berekeley National Laboratory Pathways of Matrix Self-Assembly and Mineralization Self-assembly of protein matrices and subsequent mineralization is a widespread paradigm in biology. The architecture of the underlying matrix imposes order on the nucleating mineral phase. The resulting structural complexity and mechanical properties are unparalleled in current synthetic approaches. Moreover, the vast amount of carbonate mineralization carried out by marine organisms impacts global seawater chemistry and maintains the largest terrestrial reservoir of CO2. Thus matrix assembly and mineralization impact human health and the environment, and are an inspiration to materials scientists. To understand the underlying physical controls governing matrix assembly and mineralization, we have investigated these processes using in situ AFM and TEM combined with dynamic force spectroscopy (DFS) and molecular dynamics. Our results reveal the key role played by conformational transformations in controlling the pathways and kinetics of matrix assembly. Moreover, the pathway to the final ordered state often passes through transient, less-ordered conformational states. Thus the concept of a folding funnel with kinetic traps used to describe protein folding is also applicable to matrix self-assembly. Analysis of matrix mineralization shows that nucleation is promoted through a reduction in the interfacial energy. However, nucleation via an amorphous precursor is observed at supersaturations that are too low to be explained by classical theory. The existence of pre-nucleation clusters is shown to provide a low-barrier pathway to crystallization that circumvents the large barriers to nucleation. Finally, in order to understand cluster- and particle-mediated crystallization processes, we have performed in situ high-resolution TEM. We show that when primary nuclei approach with a near-perfect lattice match, they undergo a sudden “jump to contact” over < 1nm. Measured translational and rotational accelerations show that strong, highly-direction-specific interactions drive crystal growth via oriented attachment. Taken together, these results provide new insights into the mechanisms controlling biological crystallization, from formation of the initial matrix to the maturation of final crystalline structures.
April 26, 2012 Robijn Bruinsma - UCLA Self-Assembly and Viral Shells The spontaneous test-tube self-assembly of an infectious virus from its molecular components in the 1950's is a milestone in the history of the science of self-assembly. The talk will review concepts of self-assembly that have been found useful for the analysis of the assembly and growth of viruses and the relation with other forms of self-assembly.
April 19, 2012 Mehran Kardar - MIT LEvitation by Casimir Forces in and out of Equilibrium A generalization of Earnshaw's theorem constrains the possibility of levitation by Casimir forces in equilibrium. The scattering formalism, which forms the basis of this proof, can be used to study fluctuation-induced forces for different materials, diverse geometries, both in and out of equilibrium. In the off-equilibrium context, I shall discuss non-classical heat transfer and emission by a rotating object.
April 5, 2012 Markus Deserno - Carnegie Mellon Forces Mediated By Fluid Surfaces: When Push Comes To Shove Fluid surfaces, such as the surface of water or a lipid membrane, are examples of two-dimensional structures that are captured exceptionally well by simple geometric Hamiltonians. Viewing them as "fields", to which "particles" such as colloids or proteins can bind, shows them to be vivid examples of practically relevant field theories. Moreover, they also provide endless entertainment for the theoretically minded, because their geometric origin invariably renders them nonlinear and thus analytically challenging. In my presentation I will explore how such fluid surfaces mediate interactions between particles coupling to them, and I will focus on two aspects of this problem: First, how to derive exact results for the nonlinear theory despite not being able to actually solve the underlying equations. And second, how to calculate fluctuation corrections (in the linear case) in a way that is both physically intuitive and technically efficient.
March 15, 2012 Charles Clark - National Institute of Standards and Technology and U. Maryland Photon, Atom and Neutron: How Quantum Mechanics Cracked the Nuclear Code At dawn on Thanksgiving Day of 1931, not one person in the world had a clear understanding of the essential facts of nuclear structure. Deuterium was discovered later that day using elementary quantum mechanics and atomic spectroscopy, and it provided a key clue in solving the puzzle. As we know now, deuterium, the heavy stable isotope of hydrogen, is a bound state of a proton and a neutron. However, the neutron itself was unknown at the time; it was only discovered around February 17, 1932 . The six months following the discovery of deuterium were among the most productive in the history of science, with many of the most important basic facts of nuclear structure being suddenly assembled then and then rapidly exploited. Harold Urey was awarded the 1934 Nobel Prize in Chemistry for the discovery of deuterium; eight years later the first nuclear reactor went into operation; the atom bomb was demonstrated three years after that; and the 21st birthday of deuterium was celebrated spectacularly by the detonation of the first hydrogen bomb. We are now in the 80th anniversary of this remarkable period. I will describe how some of the elementary quantum mechanics of atoms and molecules, combined with ingenious experiments, led to these extraordinary discoveries and their applications. A significant role in these developments was played by Ferdinand G. Brickwedde of the U.S. National Bureau of Standards (now the National Institute of Standards and Technology, or NIST). Some of Brickwedde's unpublished manuscripts in the collections of the NIST Library add a personal flavor to the public record of events of that time, and enhance appreciation of the roles of different branches of science in the great age of nuclear discovery.
March 1, 2012 Hank Sobel - UC Irvine Results from the T2K Neutrino Oscillation Experiment The Japan-Proton Accelerator Research Complex (J-PARC) was constructed in Tokai, Japan from 2001 to 2008. Its high-luminosity, 30-GeV proton synchrotron offers the possibility of creating a very intense neutrino beam with extremely attractive features for precision measurements and direct tests of our understanding of neutrino mixing. The first neutrino event in the multi-detector T2K experiment was observed in 2010. The experiment is optimized to detect electron neutrino interactions at the precise energy of maximum muon neutrino disappearance. This experiment will test what seems to be the only small angle (theta_13) in the neutrino mixing matrix. In addition, this experiment will precisely measure muon neutrino disappearance and may find the first evidence that the large muon-to-tau-neutrino mixing (theta_23) is not fully maximal. I will describe the experiment and discuss results from the first year of operation in which there is evidence that theta_13 may be non-zero
February 23, 2012 David Hofman - U Illinois Chicago Looking at the Hottest Points in the Universe We are currently embarking on a new frontier in research that looks at what happens when we heat a small region of space the size of a gold or lead nucleus so high that normal matter, comprised at its core of protons and neutrons, dissolves into its constituent parts, the quarks and gluons, and creates something new: “a quark gluon plasma”. We have spent the last decade creating and studying these short-lived heavy-ion hot-spots at the Relativistic Heavy Ion Collider. I will look briefly back at some of the highlights of this seminal work including how, contrary to expectation, we discovered an amazing liquid-like plasma that was also opaque to high-energy particles and appears to undergo a rapid expansion, in some ways reminiscent of theories of the early universe. We will then move to the next frontier at the world’s newest super-collider, the Large Hadron Collider, where I will show some of the exciting first results that give us a glimpse into how nature behaves in heavy-ion collisions at what is likely the hottest point in the Universe.
February 16, 2012 Joel Moore - UC Berkeley and LBNL New Topologically Ordered Phases of Condensed Matter Much of condensed matter physics is concerned with understanding how different kinds of order emerge from interactions between a large number of simple constituents. In ordered phases such as crystals, magnets, and superfluids, the order is understood through "symmetry breaking": in a crystal, for example, the continuous symmetries of space under rotations and translations are not reflected in the ground state. A major discovery of the 1980s was that electrons confined to two dimensions and in a strong magnetic field exhibit a completely different, topological type of order that underlies the quantum Hall effect. Topological order was recently discovered following theoretical predictions in some three-dimensional materials, dubbed "topological insulators", in zero magnetic field. Spin-orbit coupling, an intrinsic property of all solids, drives the formation of the topological state. This talk will explain what topological order means, how topological insulators were predicted and discovered, and how they realize the "axion electrodynamics" studied by particle physicists in the 1980s. Connections to other fields and possible applications of these new materials are discussed in closing.
February 9, 2012 David Cassidy - UC Riverside Antimatter Experiments in a University Laboratory Although antimatter is routinely created and studied at large accelerator facilities like CERN, Fermilab or RHIC, in university laboratories only those antiparticles (positrons) emitted from the decay of radioactive isotopes are generally available. A typical positron beam made from this kind of source will have a current of around 1 pA, which severely limits the kind of experiments that may be performed. However, developments in the technology of positron traps and accumulators have made it possible to use these weak beams to generate intense positron pulses, and instantaneous currents of around 10 mA may be obtained. When such bursts of positrons are implanted into suitable materials they generate a gas of the “exotic” atom positronium (chemical symbol Ps), the bound state between a positron and an electron. Although Ps is metastable and will self-annihilate in around 100 nanoseconds, it is possible to modify the rate at which this happens using pulsed lasers. In this way we can perform spectroscopic measurements of the hydrogen-like structure of Ps, and also measure various properties of these atoms, such as their kinetic energy or diffusion rates. Using a strong magnetic field to compress the positron beam spatially we can obtain Ps densities that allow for Ps-Ps interactions, and hence for the production of molecules of positronium, Ps2, which can be detected spectroscopically via an excited state. In this talk I will outline the methods we use to do these experiments, present some of our recent results and discuss our future plans.
February 2, 2012 Hassan Jawahery - Maryland The bottom quark as a probe of New Physics A new era in particle physics has begun with the main focus of the field now turned to the discovery of physics beyond the Standard Model. While, the Standard Model has, thus far, passed all tests to very high accuracy, there are many indications that it is an incomplete theory. Direct searches for new physics beyond the Standard Model, in the form of new types of elementary particles and interactions, are underway at experiments at the CERN LHC collider. The reach of these searches is in the multi-TeV energy scale that is currently reachable at the LHC. Another powerful approach, historically responsible for some of the major discoveries in the field, is the indirect detection of the imprints of New Physics through virtual quantum effects. Precision measurements of such processes can provide complementary information on possible New Physics signatures that may emerge at the LHC, but also provide a window into physics at energy scales far exceeding those available to the direct searches. On the experimental front, the measurements of these rare processes often require particle collisions at extremely high intensity. In this talk, I will describe the prospects for indirect searches for new physics and new sources of CP violation by using the bottom quark as a probe. I will also describe some of the key experimental breakthroughs that have made it possible to design and develop a very high luminosity electron-positron collider that allows for precision measurements of New Physics effects in the decays of particles containing the bottom quark.
January 19, 2012 Michael Cooper - UC Irvine Spectroscopic Surveys at z ~ 1: Understanding Environment's Role in the Decline of the Cosmic Star Formation Rate and the Rise of the Red Sequence Evolution in the global galaxy population over the past 10 Gyr has been dominated by two principal trends: a dramatic decline in the average level of star-formation activity combined with a substantial growth in the stellar mass density within the red galaxy population. While both of these evolutionary trends are well measured at z < 1, the physical mechanisms responsible remain somewhat poorly understood. Using data from the DEEP2 and DEEP3 Galaxy Redshift Surveys in concert with complementary observations spanning UV to radio wavelengths, I will present recent results that directly constrain the physical processes driving the global transformation in galaxy properties at z < 1. In particular, I will discuss ongoing work to probe the cold gas component of star-forming galaxies at high redshift, which is providing direct constraints on the fuel supply for star formation when the Universe was less than half its current age. Finally, I will conclude by outlining the limitations of the current data sets and how they might be overcome with future ground- and space-based facilities.
January 12, 2012 JoAnne Hewitt - SLAC Discovering the Quantum Universe: The Role of the Large Hadron Collider We are on the verge of a revolution in our understanding of the universe. At this time, a special opportunity is at hand to address the fundamental nature of the quantum universe through astrophysical observations, in underground experiments, and at particle accelerators. Here, I will focus on the special role of particle colliders, which recreate the conditions in the first instants after the Big Bang. The Large Hadron Collider is providing the first clear look at higher energy scales. We expect that the LHC experiments will find new particles never before observed. These particles serve as messengers, telling profound stories about the universe. I will highlight recent results of the LHC in the hunt for the Higgs Boson and Supersymmetry.
December 1, 2011 Tofigh Heidarzadeh - UCR and Huntington Library The Interplay of Theology and Cosmology in the 17th and 18th Centuries Newton demonstrated that comets undergo extreme temperature changes in their journey around the sun. In this culture, although most of the planets were assumed habitable, comets were not. During the 18th and 19th centuries, the idea of the habitability of the worlds became increasingly popular, based on contemporary theological and physical arguments. In this talk, I demonstrate how theology affected the astronomy culture at the time and helped to develop the scientific thought, leading to the theories about the habitability of the comets.
November 17, 2011 Luis Ho - Carnegie Observatories Coevolution of Black Holes and Galaxies: Recent Developments I will review observational progress in defining and refining the various empirical scaling relations between black hole masses and host galaxy properties. I will emphasize ways in which the intrinsic scatter can be quantified and present evidence that the scatter correlates with physical properties. I will discuss how to extend the scaling relations to active galaxies, and summarize preliminary efforts to probe the evolution of these scaling relations with redshift. I will present new measurements of the cold ISM content in AGN host galaxies, and constraints they place on currently popular models of AGN feedback. Lastly, I will discuss a new class of low-mass black holes in bulgeless and dwarf galaxies that serve as local analogs of seed supermassive black holes.
November 10, 2011 Bahram Mobasher - UC Riverside The Search for Dark Energy: Past, Present and the Future Discovery of dark energy is one of the most important advances in modern physics in recent years. This has direct implications towards understanding the evolution of our Universe and its future destiny, as well as in fundamental physics. In this talk I will review observational evidence for dark energy and present efforts to understand its nature. I will talk about an on-going project, using new instruments on the Hubble Space Telescope, to identify Supernovae Type Ia at the highest redshifts to study the nature of dark energy and its evolution with cosmic time. I show how this can be used to constrain the equation of state of the Universe. I will discuss future Dark Energy Missions and plans to further understand the nature of this mysterious energy.
October 27, 2011 Asantha Cooray - UC Irvine The Dusty Universe Unveiled by the Herschel Space Observatory Herschel is a European Space Agency (ESA) space observatory with important participation from NASA. In this talk I will summarize US contributions to the SPIRE instrument, one of the three instruments on the Herschel's focal plane. SPIRE has been carrying out a variety of imaging surveys at far-infrared wave lengths between 250 and 500 microns. I will discuss science results from these surveys, focusing on the properties of the dusty star-burst galaxies, their spatial distribution and the nature of lensed and distant galaxies discovered by the Herschel so far.
October 20, 2011 David K. Campbell - Boston University Transfer of Bose-Einstein Condensates through Discrete Intrinsic Localized Modes in Optical Lattices Atomic Bose-Einstein condensates (BECs) trapped in optical lattices (OLs) have been the subject of great recent experimental and theoretical interest, both in their own right and as analog models of certain solid state systems. Recent studies of the leakage of a BEC trapped in an OL have shown that localized nonlinear excitations known as “Intrinsic Localized Modes” (ILMs) can prevent atoms from reaching the leaking boundaries, thereby slowing the decay of the condensate. In this talk I report the results of a recent study (conducted with Holger Hennig and Jerome Dorignac) of this problem. To understand the mechanism by which these ILMs enhance the trapping, we study the case of atom transport —“tunneling”—through a ILM on a nonlinear trimer. We show that this transport is related to the destabilization and subsequent motion of ILM and that there exists a threshold in the total energy on the trimer that controls this destabilization. We find that this threshold and the resultant tunneling can be described analytically by defining a three-dimensional “Peierls-Nabarro” energy landscape which restricts the dynamics of the trimer to a limited region of phase space. We further establish that the value of the threshold is related to the Peierls-Nabarro barrier of a single ILM. We then embed our nonlinear trimer in an extended lattice and show numerically that the same destabilization mechanism applies in the extended lattice. Our results suggest a possible means for controlling the transmission of coherent atomic beams in interferometry and other processes.
October 13, 2011 Matthew Malkan - UCLA Measuring Cosmic Evolution: How to Find the Distant Galaxies? Figuring out galaxy evolution, like much of astronomy, depends on which methods we use. What we want is an unbiased survey of galaxies over a large cosmic volume, uniformly distributed with cosmic time. This is a great observational challenge. I will present a two-step approach towards meeting this goal. One is using galaxies in the Subaru Deep Field, at the 'desert crossroads' of redshift z=1.5--2.5. By combining all the leading photometric methods for a very large sample, this work has given us a reasonably complete view of galaxies across that crucial cosmic epoch. The second method constitutes of a radically different approach, using infrared SPECTRA of all galaxies in a deep field, without any photometric pre-selection whatever. We are now doing this with on the Hubble Space Telescope with the WFC3 Infrared Spectroscopic Parallels (WISP) survey. By exploiting HST's unmatched capability for slitless spectroscopy in the Infra- Red, WISP is surveying a large population of extreme line-emitting galaxies. They are too faint to be noticed by standard photometric searches, but account for a lot of the integrated cosmic star formation history. The many thousands of WISP galaxies include large numbers of extreme- starburst dwarfs, with low metallicity-- possible building blocks of modern galaxies.
September 29, 2011 Molly Peeples - Center for Galaxy Evolution, UCLA Chemical Clues to Star Formation Feedback The abundances and distributions of heavy elements inside and out of galaxies provide important insights into the circulation of baryons between the interstellar, circumgalactic, and intergalactic media. In this talk, I will discuss how the observed interstellar oxygen abundances of star-forming galaxies imply that the efficiency with which these galaxies expel their oxygen must scale steeply with galaxy mass. I will then put these predictions in context of the recent observations made with the new Cosmic Origins Spectrograph on the Hubble Space Telescope of oxygen in the circumgalactic medium of z~0 galaxies.
June 2, 2011 Barry Barish - Caltech The Next Great Particle Accelerator: A TeV Scale Linear Collider The Large Hadron Collider (LHC) at CERN is opening up the TeV energy scale for exploration. We are at the threshold of a new era in particle physics that we believe will provide strong motivation to develop a companion accelerator, a lepton collider. In anticipation, the International Linear Collider (ILC) has been conceived as that machine, and is being designed by a unique global process involving coordinated R&D and design work by leading accelerator physicists worldwide. I will discuss how a TeV scale linear collider could enable us to zoom in on the new landscape found at the LHC with great precision, revealing its richness and new layers of detail. The ILC is technically a very challenging enterprise, involving development of high gradient superconducting radio-frequency (SCRF) accelerating cavities. To achieve the required event rate will require both high power and very small emittance beams. A reference design for the ILC has been developed and I will outline the key technical features of a machine that we are designing to be built on a timescale of the early 2020s.
May 12, 2011 Jorge López - University of Texas, El Paso TBA Experiments with neutron-rich isotopes are shedding light on the role isospin plays in the equation of state of nuclear matter, and isoscaling − a straight-forward comparison of reactions with different isospin − could deliver valuable information about it. In this talk the topic of neutron rich nuclei will be introduced along with the concept of isoscaling, which will be found to be a general effect of disassembling systems. Through molecular dynamics, percolation and simple samplings, we find that indeed isoscaling can help us learn about the nuclear EoS, but only in some range of energies.
April 28, 2011 Peter Young - UC Santa Cruz Solving Optimization Problems on a Quantum Computer It is known that an eventual quantum computer could solve certain problems, such as factoring large integers, much more efficiently than any known algorithm on a classical computer. It has been proposed that a quantum computer might also be able to solve a broad range of "optimization" problems more efficiently than a classical computer using the "Quantum Adiabatic Algorithm" (QAA). In this talk I will give an introduction to quantum computers, and then describe my investigations of the efficiency of the QAA for several problems. Since we don't yet have a quantum computer, the study involves Monte Carlo simulations running on a traditional (i.e. classical) computer.
April 21, 2011 David Saltzberg - UCLA The ANITA experiment: A Million Cubic Kilometer Search for High Energy Neutrinos in Antarctica The ANITA (ANtarctic Impulsive Transient Antenna) experiment is a balloon-borne radio telescope and interferometer, designed to detect radio-Cherenkov emission from cosmic neutrinos with energies of exa-electron-volts. Such neutrino events would also allow probing the weak interaction at energy scales beyond the reach of the Large Hadron Collider. Because neutrinos are so penetrating, they offer the possibility to explore the entire high-energy universe without the usual local distance cutoff suffered by photons and protons. Our new data set allows the most sensitive investigation to date of neutrino flux models, which offers the possibility of revealing the sources of the highest energy cosmic rays. I will present the newly released results of the ANITA-II neutrino search. In addition to the neutrino search, an analysis of ANITA-I data also yielded an unexpected detection of the highest energy cosmic rays.
April 14, 2011 Arvind Rajaraman - UC Irvine The Search for Dark Matter: Direct Searches, Indirect searches and Colliders The search for dark matter is one of the outstanding problems in particle physics. I will discuss current efforts to search for this elusive particle. I will also discuss constraints that can be placed on dark matter particles from current and upcoming collider experiments like the Large Hadron Collider. These searches are complementary to current direct detection searches like XENON and CDMS, and can probe light dark matter particles which are otherwise inaccessible at direct detection experiments.
March 10, 2011 Assa Auerbach - Technion, Israel Elementary Particles of Superconductivity Historically, two paradigms competed to explain superconductivity (i) Bose Einstein Condensation of weakly interacting Charge 2e pairs (Schafroth), and (ii) Pairing instability of the Fermi liquid (BCS). BCS theory was the unquestionable winner until the late 80's. BCS approximations however, have suffered major setbacks in the advent of high temperature, short coherence length superconductors, such as cuprates, pnictides, and granular superconducting films. A third paradigm has offered itself for understanding some properties of unconventional superconductors: Hard Core lattice Bosons (HCB). HCB behave less like weakly interacting bosons or fermions, but (strangely) more like quantum spins. Their static correlations are very well understood by theories of quantum antiferromagnets. Their dynamics have only recently been explored. Recent calculations of the DC and AC conductivity and Hall conductivity of Hard Core Bosons suggests a new route to understanding strange metallic properties of unconventional superconductors in their "normal" state.
March 3, 2011 Naveen Reddy - National Optical Astronomical Observatory How Dust Affects Our View of the Distant Universe and How to Correct for It The primary by-products of stellar nucleosynthesis include heavy elements that are eleased into the interstellar medium where they can coagulate to form dust particles. I will discuss why dust is important for studying galaxy evolution and for uncovering the fundamental physics that governs the Universe. Our results suggest that galaxy growth is intimately connected with the evolution of dark matter during the first ~3 billion year history of the Universe. I will go on to show that dust in the distant Universe has a direct effect on the observed luminosity distribution of galaxies, the dustiness of a galaxy is directly correlated with its emergent UV luminosity, and that faint galaxies dominate the luminosity and star formation rate density at high redshift. I then use this information to resolve one of the outstanding problems that has plagued cosmologists over the last few years, namely the discrepancy between the star formation history and the evolution in stellar mass density of the Universe. I conclude with an overview of how future facilities like JWST and TMT, as well as forthcoming dark energy experiments, can be used to uncover the physics of faint galaxies at high redshift and unveil the complex connection between galaxies and the surrounding intergalactic medium.
February 17, 2011 Eddy Timmermans - Center for Nonlinear Studies, LANL Zero-temperature phase separation and strong coupling polarons in dilute gas Bose-Einstein condensates Ultra-cold atom traps are providing a new laboratory for the study of quantum many-body physics. We will describe how a neutral atom Bose-Einstein condensate mixture can spatially separate in a process that is a second-order phase transition while exhibiting critical opalescence-like behavior in the quantum regime. The simplest kind of such mixture, a Bose-Einstein condensate with only a single impurity (unlike) atom, behaves as a polaron. In the strong coupling regime, the impurity polaron can self-localize into a structure with an impurity extent that is smaller than the coherence length of the Bose-Einstein condensate. We show how multiple bosonic impurities can self-localize at weaker impurity-boson couplings and form a self-localized impurity droplet that is even smaller than the single impurity polaron. We identify this process with the onset of phase separation nucleation. We will discuss relevant experiments and experimental prospects for studying the self-localized polarons, a new class of BEC sub-coherence length structures.
February 10, 2011 Keith Schwab - Caltech Pursuing Quantum Mechanics in Mechanical Structures Over 30 years ago, researchers investigating the ultimate limits of mechanical detection of gravitational waves, understood theoretically how quantum mechanics should limit these ultra-sensitive mechanical measurements. In the past 10 years, the tools to prepare micron-scale mechanical structures in fundamental quantum states has been rapidly developed, using both optical and electrical techniques. In this lecture, I will give an overview of the state of the art from experiments in my group and around the world, focusing on the recent experiments to prepare the quantum ground state of motion and the success to produce superposition states in the laboratory.
February 3, 2011 Mark Morris - UCLA The Galactic Black Hole and its Entourage Diffraction-limited observing technologies at the Keck Observatory, combined with very long baseline radio interferometry, have sealed the case for a supermassive black hole at the dynamical center of our Galaxy. Our understanding of the black hole's mass accretion activity has been enhanced in recent years through direct observation of the accretion flow, although many fundamental questions remain: is there an observable jet? Does the mass inflow have a stochastically and continuously changing geometry? Which of the many suggested gas-dynamical instabilities is responsible for the strong variability of the emission from the accretion flow? What is the spin of the black hole? All these questions are now being pursued. Stepping out from the accretion flow, we have explored the dynamics of stars in the immediate vicinity of the black hole using laser guide star adaptive optics, and we are within reach of using subtle deviations from pure Keplerian orbits to measure the combined effects of General Relativity and distributed dark matter. In the meantime, we have found that the distributions of both young stars and old stars around the black hole have completely overturned theoretical expectations. I'll end with a discussion of the Next Generation Adaptive Optics project, which will provide the technology for the next great leap in spatial resolution and astrometric and photometric sensitivity, and I'll describe what breakthroughs we can expect from that for Galactic center research.
January 27, 2011 Matthew Fisher - UCSB Quantum Crystals, Quantum Choreography and Quantum Computing Seething within each of natures crystals is an exotic quantum world of electrons dancing and twirling about one another. Each crystal has its own unique choreography, as varied as the crystals themselves. In some crystals the electron dancing patterns are structured and orderly. Within others the electrons are seemingly entangled in a fluctuating web of dizzying quantum motion. In this talk I will describe the ongoing efforts to discern the quantum choreography that underlies even the most intricate of natures electron dances, and to perhaps ultimately harness such understanding to design a futuristic topological quantum computer.
January 13, 2011 Oleg Tretiakov - Texas A&M University Topological Thermoelectrics I will propose a novel way to obtain high thermoelectric figure of merit in topological insulators. The work is based on the fact that the dislocations in certain 3D topological insulators have topologically protected 1D conducting channels. We predict that at high densities of the dislocations can be dominated by these 1D states which can reduce the thermal conductivity on one hand and increase the conductivity and thermopower on the other. I will show that in principle this system can have very high of order 10, hence making it a uniquely strong candidate for applications in heat management of nanodevices.
December 2, 2010 Jon Gardner - NASA's Goddard Space Flight Center Studying Galaxy Formation with the James Webb Space Telescope In the deepest optical to infrared observations of the universe, galaxies are seen at redshifts z > 6, less than 1 Gyr after the Big Bang, at the end of a period when light from the galaxies has re-ionized Hydrogen in the inter-galactic medium. These observations, combined with theoretical understanding, indicate that the first stars and galaxies formed at z > 10, beyond the reach of the Hubble and Spitzer Space Telescopes. To observe the first galaxies, NASA is planning the James Webb Space Telescope (JWST), a large (6.5m), cold (<50K), infrared-optimized observatory which will orbit around the second Earth-Sun Lagrange point. JWST will have four instruments: The Near-Infrared Camera, the Near-Infrared multi-object Spectrograph, and the Tunable Filter Imager will cover the wavelength range 0.6 to 5 microns, while the Mid-Infrared Instrument will do both imaging and spectroscopy from 5 to 28.5 microns. In addition to JWST’s ability to study the formation and evolution of galaxies, I will also briefly review its expected contributions to studies of the formation of stars and planetary systems. I will conclude with a description of recent technical progress in the construction of the observatory.
November 18, 2010 Scott Currie - UCR, Dept. of Cell Biology and Neuroscience Spinal Control of Limb Movement; A vertebrate Model The coordinated rhythmic movements that all animals produce (e.g., walking, swimming, breathing, scratching), are characterized by precise tempo-spatial sequences of muscle activity, referred to as “motor patterns.” Motor pattern sequences are constructed by rhythmically active networks of nerve cells that synaptically interact with each other, called “central pattern generators” (CPGs) in the central nervous system. I study network-level mechanisms utilized by spinal cord CPGs in turtles to generate coordinated scratching and swimming movements of the limbs. In this talk I present my latest research involving (1) pre-motor command systems in the turtle brainstem that activate locomotor CPG networks in the spinal cord, and (2) the coordinated limb movements and muscle activity patterns that underlie lateral turning maneuvers during turtle swimming. Animal locomotion in water, air, or terrestrial environment exhibits a variety of continual fine adjustment in steering as well as more abrupt turns and directional reversals. During swimming, in which the animal is free to move in 3 dimensions, locomotor adjustments can involve changes in yaw, pitch and roll orientations. We found that stereotyped turning behavior can be elicited by slowly rotating turtles in the horizontal plane via a motorized clamp encircling the shell. We are also developing isolated preparations of the turtle brainstem and spinal cord that will express turning activity to study these underlying mechanisms at a cellular level.
November 4, 2010 David K. Campbell - Boston University The Fermi Pasta Ulam (FPU) Problem and the Birth of Non-linear Science In 1953, Enrico Fermi, John Pasta, and Stan Ulam initiated a series of computer studies aimed at exploring how simple, multi-degree of freedom nonlinear mechanical systems obeying reversible deterministic dynamics evolve in time to an equilibrium state describable by statistical mechanics. Their expectation was that this would occur by mixing behavior among the many linear modes. Their intention was then to study more complex nonlinear systems, with the hope of modeling turbulence computationally. The results of this first study of the so-called Fermi-Pasta-Ulam (FPU) problem, which were published in 1955 and characterized by Fermi as a “little discovery,” showed instead of the expected mixing of linear modes a striking series of (near) recurrences of the initial state and no evidence of equipartition. This work heralded the beginning of both computational physics and (modern) nonlinear science. In particular, the work marked the first systematic study of a nonlinear system by digital computers (“experimental mathematics”) and led directly to the discovery of “solitons,” as well as to deep insights into deterministic chaos and statistical mechanics. In this talk, I will review the original FPU studies and show how they led to the understanding of two key paradigms of nonlinear science. Specifically, I will show how a continuum approximation to the original discrete system led to the discovery of “solitions” whereas a low-mode approximation led to an early example of “deterministic chaos.” I will close with a brief indication of how the recurrence phenomenon observed by behavior by FPU can be reconciled with mixing, equipartition, and statistical mechanics.
October 28, 2010 Jun Zhu - Penn State Controlling the Property of Graphene with Adatoms I will discuss our work on fluorinated graphene. In the limit of very dilute fluorination, fluorinated graphene undergoes a carrier density driven metal-insulator transition, exhibiting weak localization at high densities and variable range hopping at low densities. In the hopping regime, the system displays a very large negative magnetoresistance in a perpendicular magnetic field. The zero field resistance is reduced by up to a factor of 40 and has yet to saturate at 9 Tesla. Possible explanations include adatom-induced magnetism and interference-driven Anderson localization. In the opposite limit of full fluorination, we demonstrate the synthesis of nanocrystalline graphene monfluoride, CF. We show evidence of the structure and vibrational modes of CF . Transport measurements indicate a large band gap with strongly insulating behavior. Photoluminescence studies reveal several emission modes in the visible range. Their temperature dependence points to sub gap defect states. The band edge emission of CF has yet to be found, likely in the deep UV.
October 21, 2010 Lincoln Carr - Colorado School of Mines Macroscopic Superposition States in Bose−Einstein Condensates It is vital not to take our most fundamental physical theories for granted. For example, researchers have looked for deviations from the gravitational inverse square law at very small sub-micron length scales. Similarly, one can ask what predictions of quantum mechanics might break down in untested regimes. Since the classical world is macroscopic and the quantum world is microscopic, a natural place to test quantum mechanics is in mesoscopic physics. Macroscopic superposition is a largely untested mesoscopic prediction of quantum mechanics. An excellent candidate for macroscopic superposition states, also called Cat (or NOON) States after Schrodinger’s famous gedanken experiment, is a Bose-Einstein condensate in a double well. Mathematically, this is a fifty year old quantum many body problem. The experimental context of Bose-Einstein condensates gives one hope to observe the first truly large scale Cat States of matter. We show that Bose-Einstein condensates require two new energy scales. We introduce the role of the dimensionality of each well. We demonstrate that the many body wavefunction serves to protect Cat States from decoherence. Finally, we present a practical scheme for dynamic realization of such states.
October 14, 2010 Gillian Wilson - UCR The Biggest, Baddest Babies in the Nursery: What we are Learning about Distant Clusters of Galaxies from the SpARCS Survey Clusters of galaxies are the most massive gravitationally bound structures in the Universe, and provide excellent laboratories for testing both galaxy evolution and cosmological theories. New infrared and optical capabilities are facilitating large, homogeneous cluster surveys at high redshift. The Spitzer Adaptation of the Red-sequence Cluster Survey (SpARCS) is a 25-night three-year deep z'-band imaging survey in the Spitzer SWIRE Legacy fields. Now complete, SpARCS is currently the largest z > 1 cluster survey, and has discovered hundreds of new cluster candidates using the Cluster Red-Sequence technique. I will show examples of newly discovered, spectroscopically confirmed rich clusters. I will also discuss The Gemini Cluster Astrophysics Spectroscopic Survey (GCLASS), a comprehensive multiwavelength survey of 10 massive SpARCS clusters. The backbone of GCLASS project is a 220 hr spectroscopic campaign using the GMOS instruments on Gemini North and South. When complete in early 2011, GCLASS will be the largest survey ever carried out using the Gemini 8-meter telescopes, and will have obtained spectra for ~600 cluster galaxies. I will present an overview of the GCLASS survey, and explain what it is revealing about these massive structures in formation. I will also show examples of SpARCS clusters thought to be at even higher redshift than the GCLASS sample, and for which we have been awarded time for spectroscopic follow-up on the Keck and VLT telescopes this winter. I will end by discussing the challenges and rewards of utilizing SpARCS and other cluster surveys to constrain cosmological parameters.
October 7, 2010 Noel Swerdlow - University of Chicago / Caltech Galileo’s Contribution to Astronomy and the Consequent Conflict with the Church Galileo Galilei made many important contributions to the science, in particular to astronomy. He invented the first telescope, made detailed observations of solar system planets and from observations of phases of the Venus, concluded that the Earth is moving around the Sun. His discoveries at the time led to direct conflict with the church. The story of Galileo’s debate with the church is among the most fascinating in the history of science.
June 3, 2010 Ted Einstein - University of Maryland Steps on Surfaces, Their Significance, and Their Evolution: From Elementary Models to Universal Properties Steps on surfaces have many practical uses; I begin with a survey of intriguing phenomena. Steps also offer remarkable, quantitatively measurable realizations of some familiar physical models. Step dynamics, e.g., can be viewed as a form of Brownian motion. I focus on the statistical properties of interstep separations on misoriented ("vicinal") surfaces. Such a terrace-width distribution (TWD) can be related to the spacing distribution of repelling fermions in one dimension. The TWD can then be analyzed simply in terms of undergraduate quantum mechanics and with more sophistication in terms of general properties of equilibrium fluctuations, viz. generalizations of the amazingly broadly applicable Wigner distribution from random-matrix theory. Finally, I briefly discuss our recent efforts to go beyond equilibrium to describe step relaxation, growth, and capture-zone (Voronoi cell) distributions in island growth, with remarkable experimental implications.
May 20, 2010 Gail Hanson - UCR WHAT WILL WE DISCOVER FIRST? THE BEGINNING OF PHYSICS AT THE LARGE HADRON COLLIDER AT CERN The Large Hadron Collider (LHC) at CERN, the world’s largest and highest-energy particle accelerator, has begun operation, more than 20 years after its conception and 10 years of construction. The LHC will replicate conditions that existed less than one-billionth of a second after the Big Bang and will test theories concerning the origin and evolution of the Universe. Physicists from UCR are part of a large team of physicists who built the Compact Muon Solenoid, one of the four huge LHC experiments, and are now collecting data from proton-proton collisions at more than three times the energy of any previous accelerator. We expect to create particles that have never before been observed. Possible discoveries will revolutionize particle physics, for example by providing explanations for the origin of mass and for the mysterious dark matter that makes up most of the mass of the Universe.
May 13, 2010 Michael Devirian - JPL Staring Too Close To the Stars A subject of speculation for centuries, in the past fifteen years ingenious methods have been devised to actually detect the presence of planets around stars other than our sun. Over 453 such "exoplanets" have now been identified. The "holy grail" of the exoplanet search remains the detection and characterization of planets that, like our Earth, orbit in the habitable zone of their star where liquid water can exist, have a mass that allows a rocky or ocean surface and that show signs of biological activity. The core problem is that habitable planets lie very close to their star, as viewed from Earth, and are much dimmer, so that the starlight blinds the observer. This talk will discuss what NASA is doing to develop technology and missions that will let astronomers "stare too close to the stars" and find the evidence for life on new worlds.
May 6, 2010 Alexander Korotkov - UCR Partial collapse and uncollapse of a wavefunction: theory and experiments We discuss a question controversial for decades: what is "inside" the quantum state collapse due to measurement, and what happens if the collapse is stopped half-way. For particular setups with solid-state qubits the answer is rather simple: the qubit state changes in accordance with gradually acquired information, without loss of its purity (no decoherence). The simple theory of such measurement leads to a number of experimentally testable predictions. For example, it shows that Rabi oscillations are non-decaying (persistent) if they are continuously weakly measured. The theory also shows that a partial collapse due to a weak quantum measurement can be probabilistically undone, fully restoring ("uncollapsing") an arbitrary initial state. These effects can be potentially useful for quantum feedback, decoherence suppression, etc. So far three such experiments have been realized: partial collapse of a superconducting phase qubit, uncollapse of a phase qubit, and persistent Rabi oscillations in a superconducting charge qubit.
April 29, 2010 Rene Ong - UCR VERITAS Explores the TeV Gamma-Ray Sky Our understanding of the very high energy (VHE; E>100 GeV) universe has progressed rapidly during the last few years as a result of new instruments and exciting discoveries. In particular, ground-based telescopes, such as VERITAS in southern Arizona, have discovered many astrophysical sources of VHE gamma rays, including supernova remnants, binary star systems, blazars, and radio galaxies. These telescopes are also carrying out sensitive searches for the annihilation of particle dark matter. Similar exciting results are arriving from the recently-launched Fermi Gamma-ray Space Telescope. This talk will overview what we know about the VHE universe and describe recent exciting results from VERITAS. The future prospects for the field will be summarized.
April 15, 2010 George Coutrakon - Northern Illinois University Proton Therapy in the United States: past, present, and future. Proton beam therapy has matured rapidly in the last decade as a state of the art treatment for many cancers. Protons have demonstrated efficacy, and in many cases , superior outcomes for cancer treatments. Dr. Robert Wilson, an accelerator physicist and first director of Fermi National Accelerator Laboratory, first proposed protons for use in cancer treatment in 1946. However, most of the advances with proton beam therapy had to await the advent of CT and MRI imaging to "see" the tumor and healthy organs with the same accuracy that proton doses were capable of delivering. This talk will explore the evolution of proton beam and heavy ion therapy and discuss where we are now and how the field is evolving towards the future.
April 8, 2010 Clifford Johnson - USC Surprises at Strong Coupling and How to Cope The last six years have seen some remarkable phenomena emerging from experimental systems in diverse areas of physics - nuclear, atomic, and condensed matter - over an impressive range of temperatures (from micro Kelvin to several trillion Kelvin - 19 orders of magnitude), densities (26 orders of magnitude), and experimental scales (desktop experiments to giant particle accelerators 4 km around). These experiments have uncovered a new type of behaviour for matter, that appears at extremely strong coupling, in a variety of systems. The traditional techniques for understanding these systems have proven unequal to the task of modelling or predicting many of the properties uncovered. Perturbation theory fails, and various strong coupling techniques also fail. This talk will describe an exciting new set of powerful tools that seem to capture much of the new strongly coupled physics, and may point the way to new phenomena and insights into various important emergent phenomena at strong coupling, such as high-temperature superconductivity and quantum phase transitions.
April 6, 2010 Eva Andrei - Rutgers University Grapehene: relativistic electrons in carbon flatland The recent discovery of graphene, a one-atom thick membrane of crystalline Carbon, has opened an extraordinary arena for new physics and applications stemming from charge carriers that are governed by quantum-relativistic dynamics. I will review the physical properties of this material and present recent experimental results obtained with scanning tunneling microscopy and magneto-transport which provided access to the unusual charge carriers in graphene. The findings include direct observation of the Landau level energy spectrum that governs the motion of the relativistic charge carriers in a magnetic field, observation of the fractional quantum Hall effect and a magnetically induced insulating phase.
March 11, 2010 Nai-Chang Yeh - Caltech
March 4, 2010 Tim Lyons -
February 25, 2010 Chandra Varma - UC Riverside Quantum Phase Transitions or How to Love Singularities In recent years, a variety of phenomena in systems of interacting fermions is understood by fluctuations towards phase transitions to a broken symmetry in the limit of zero temperature. For example, the high temperature superconductivity phenomenon is known to be associated with such fluctuations. These fluctuations require a quantum-mechanical theory unlike the theory of fluctuations near classical phase transitions which is one of the great and beautiful solved problems of the 20th century. I will try to provide a simple and concise account of the difference between classical and quantum phase transitions and fluctuations.
February 18, 2010 Feng Wang - UC Berkeley Tunable Electronic and Optical Properties of Graphene Graphene, a single layer of carbon atoms, exhibits novel two-dimensional electronic behavior. Importantly, the unusual graphene physics can be controlled. In this talk, I will show how we can vary optical transitions in monolayer graphene and control the bandgap in bilayer graphene through electrical gating. I will also describe an unusual tunable phonon-electron Fano resonance in bilayer graphene.
February 11, 2010 Phil Collins - UC Riverside Single molecule circuits with carbon nanotube wiring The vision for molecular electronics extends well beyond miniaturation and scaling to include new techniques for studying chemical bonding, biocatalysis, and molecular recognition. However, operational single molecule devices remain exceedingly fragile and difficult to fabricate. We have demonstrated a promising new architecture for studying single molecule behavior based on “point functionalization” of single-walled carbon nanotube circuits. In this technique, single defects are created in the sidewall of an electrically connected nanotube. The defects provide an ideal test platform for studying the physics of one dimensional transport, as well as being attachment sites that enable the electrical monitoring of single molecule dynamics. This presentation will describe these techniques and demonstrate real-time monitoring of single molecule processes including oxidation, conjugation, recognition and binding.
January 21, 2010 Steve Kivelson - Stanford
January 14, 2010 Nadya Mason - UIUC Superconducting Tunneling Spectroscopy of Carbon Nanotubes Carbon nanotubes, or one-dimensional wires made of carbon, have been considered leading candidates for the study and application of nanoscale electronics. However, work on these systems has been limited by difficulties in probing and controlling devices, particularly in the quantum regime. In this talk, I will discuss transport experiments on carbon nanotube quantum dots and wires, focusing on results from a new three-probe technique which uses a superconducting tunnel probe. The superconducting probe enhances weak spectroscopic features and the multiple probes allow the effects of bias to be directly determined. In particular, superconducting tunneling techniques applied to carbon nanotube quantum dots show an enhancement of weak tunneling processes, as well as unexpected scattering when an end-to-end bias is applied. I will also discuss measurements of the shape of the electron energy distribution functions, and hence energy relaxation rates, in nanotubes that have bias voltages applied between their ends. These measurements give insight into electron interactions in carbon nanotubes, and are relevant to applications that use nanotubes as quantum devices. Finally, I will discuss new results from extending the superconducting tunneling technique to graphene. In general, tunneling spectroscopy with a superconducting probe may be a powerful new tool for characterizing electron behavior in carbon nanostructures.
December 3, 2009 Alison Coil - UCSD CLustering, Quenching, and Feedback: Galaxies and AGN at z = 1 Roughly half of the red elliptical galaxies observed today have formed since z=1. I will present galaxy clustering results from the DEEP2 Redshift Survey that strongly constrain the mechanism responsible for the quenching or cessation of star formation in these galaxies. I will show where this quenching is occurring on large scales and how it can not be due primarily to cluster-specific physics. I will also present results on the clustering of optically-bright quasars and X-ray selected AGN at z=1. I will show new results on the prevalence of outflowing galactic winds at z=1 and discuss their role in quenching star formation. Finally, I will present a new wide-area prism survey that will allow further studies of galaxy evolution to z=1 with the largest faint galaxy survey to date.
November 19, 2009 Phillip Kim - Columbia University Pseudo Spins in Graphitic Carbon Nanostructures: From Analogy of Relativistic Quantum Mechanics to Carbon Based Electronics Carbon based graphitic nanomaterials have been provided us opportunities to explore fundamental transport phenomena in low-energy condensed matter systems to reveal interesting analogy to the relativistic quantum mechanics. The unique electronic band structure of graphene lattice yields a linear energy dispersion relation where the Fermi velocity replaces the role of the speed of light and pseudo spin degree of freedom for the orbital wavefunction replaces the role of real spin in usual Dirac Fermion spectrum. In this presentation we will discuss experimental consequence of charged Dirac Fermion spectrum with pseudo spin structure in two representative low dimensional graphitic carbon systems: 1-dimensional carbon nanotubes and 2-dimensional graphene. Combined with semiconductor device fabrication techniques and the development of new methods of nanoscaled material synthesis/manipulation enables us to investigate mesoscopic transport phenomena in these materials. The exotic quantum transport behavior discovered in these materials, such as ballistic charge transport and unusual half-integer quantum Hall effect both of which appear even at room temperature.
November 12, 2009 George Helou - Spitzer Science Center, Caltech The Spitzer Space Telescope: The history and science highlights Abstract
November 5, 2009 Jeff Cooke - Caltech High Redshift Galaxies: Why Should We Care? In the widely accepted galaxy formation scenarios, massive galaxies observed around us today, were formed from the merging of a series of smaller systems over cosmic time. Although this is a highly successful theory, consistent with high-resolution cosmological simulations, direct observation of this process has been challenging. This is especially true at high redshifts, where galaxies are fainter and less resolved and where, to date, we have been restricted to morphological identification in the less-understood redshifted rest-frame ultraviolet wavelengths. I will discuss recent work, showing that the ultraviolet Lyman-alpha transition of hydrogen and associated spectral features provide a unique indicator of high-redshift galaxy interactions during the critical epoch of their formation (2 < z < 6). Detailed analyses of space-based morphology and ground-based imaging and spectroscopy indicate the presence of a bi-modality in high-redshift systems, implying two different formation paths that could lead to the two distinct populations of galaxies seen today. I will present a simple technique to select very large numbers of high-redshift galaxies having desired Lyman-alpha behavior and associated properties from "cheap and deep" broadband imaging. Fundamental properties, such as spatial distribution, mass, and typical star formation rates can be achieved from such large samples to test these implications, enabling a connection between forming galaxies in the early universe and present-day galaxies such as our own Milky Way.
October 29, 2009 Shan-Wen Tsai - UCR Quantum Phases of Cold Atom Mixtures I will give an introduction to the field of cold atom physics where remarkable advances in cooling and manipulation techniques have allowed probing quantum gases at micro-Kelvin down to nano-Kelvin temperatures. The parameters of the microscopic Hamiltonian of these systems can be controlled and tuned by means of external fields, including the creation of artificial lattices in one, two, and three dimensions. I will present some recent results from my research group on theoretical studies of quantum phases of mixtures of cold atoms with different quantum statistics (Bosons and Fermions), with emphasis on mediated interactions and quantum many-body effects, and discuss some future directions.
October 22, 2009 Ivan K. Schuller - UCSD Nanostructures: Confinement, Proximity and Induced Phenomena Physics in confined geometries is one of the most active areas of research in Solid State and Materials Physics. The extensive activity in this field is driven by the fact that physical length scales are close to structural sizes, which can be controlled using modern thin film and lithography techniques. In addition, a number of applications in the areas of information storage. medicine and sensors have moved basic research results into the application area in a very short period of time. I will describe a variety of representative basic research results, which illustrate some of the exciting and novel results when magnetic and superconducting materials are confined into small dimensions. Interesting effects are observed when these dimensions are comparable to magnetic length scales such as dipolar, exchange, and domain sizes and superconducting length scales such as the penetration and coherence lengths. Experiments relate to confinement effects due to quantum mechanical quantization, a variety of proximity effects in which dissimilar materials have strong effects on each other and phenomena which are induced by external means such as electric and magnetic fields, light, etc. More specifically, I will describe studies of confinement, proximity and induced phenomena in nanostructured magnetic systems. Particularly interesting phenomena were observed in the collective superconducting pinning by arrays of nanostructured magnetic dots in a different configurations and shapes. As these systems are driven away from equilibrium they exhibit interesting unexpected response, unlike observed in naturally occurring materials.
October 15, 2009 Peter Capak - Caltech Probing the formation of the first galaxies Recent advances in ground and space based near-infrared imaging are giving us the first glimpses of galaxy formation in the early universe. However, considerable uncertainty remains in how these objects are formed and what their present day counterparts are. I will begin by outlining what we know about the universe when it was ~1/3 its present age (z~2) and what constraints this places on the process of galaxy formation at higher redshift. Then, using multi- wavelength data and deep spectroscopy from the 10m Keck telescopes I will show that the number and mass of galaxies appears to be growing rapidly between 400 million and 1.5 billion years after the big bang (44). Finally, using deep wide-field near-infrared data I will examine the population of galaxies in the first 2-300 million years after the big bang (9
October 8, 2009 James Bullock - UC Irvine Dwarf Galaxies, Dark Matter, and the Threshold of Galaxy Formation Over the past five years, searches in Sloan Digital Sky Survey data have more than doubled the number of known satellite galaxies orbiting around the Milky Way disk,revealing a population of ultra-faint systems with total light output barely reaching ~1000 times that of the Sun. These newly-discovered dwarf galaxies represent galaxy formation in the extreme. They are not only the faintest galactic systems known but they are also the most dark matter dominated and most metal poor galaxies in the universe. Completeness corrections suggest that we are poised on the edge of a vast discovery space in galaxy phenomenology, with hundreds more ultra-faint galaxies to be discovered as future instruments hunt for the low-luminosity threshold of galaxy formation. I discuss how dark matter dominated dwarfs of this kind probe the small-scale power- spectrum and offer a particularly useful target for dark matter indirect detection experiments.
June 4, 2009 Brad Marston - Brown University The Quantum and Fluid Mechanics of Global Warming Quantum mechanics plays a crucial, albeit often overlooked, role in our understanding of the Earth's climate. In this talk three well known aspects of quantum mechanics are invoked to present a simple physical picture of what may happen as the concentrations of greenhouse gases such as carbon dioxide continue to increase. Historical and paleoclimatic records are interpreted with some basic astronomy, fluid mechanics, and the use of fundamental laws of physics such as the conservation of angular momentum. I conclude by discussing some possible ways that theoretical physics might be able to contribute to a deeper understanding of climate change.
May 28, 2009 Utpal Sarkar - Physical Research Laboratory, Ahmedabad, India Astroparticle Physics, Neutrinos and LHC
May 21, 2009 Richard Seto - UC Riverside Cooking Nuclear Matter What happens when you take matter and heat it to extreme temperatures? - perhaps 1012 Kelvin - the temperature of the early universe a few microseconds after its birth. Fermi speculated about matter in such unusual questions in his notes on Thermodynamics.These temperatures are such that some of the basics building blocks of matter known to us- protons and neutrons - would melt into their basic constituents -quarks and gluons - a quark-gluon plasma. Experiments at the Relativistic Heavy Ion Collider at the Brookhaven National Laboratories and at the LHC at CERN, are capable of reaching such temperatures.
May 7, 2009 Allen Mills - UC Riverside Positronium Bose-Einstein Condensation and Stimulated Annihilation
April 23, 2009 Paco Guinea - Instituto de Ciencia de Materiales de Madrid, Spain Electrons in Two Dimensions: Models for Graphene Graphene is a fascinating two dimensional material, which forms the building block of graphite. It shares features with materials such as carbon nanotubes and fullerenes, and also with artificial devices, like MOSFETs and quantum wells. Electrons in graphene move as massless particles, and they show many unusual properties, such as the existence of "fictitious" gauge fields, localized states, and new effects due to the electron-electron interactions. Many properties of graphene are highly sensitive to the outside environment. Models to describe some of the basic properties of graphene, and a review of outstanding challenges will be presented.
April 9, 2009 Graciela Gelmini - UCLA In Search of Dark Matter Particles: Have We Found Them? We know a lot about dark matter but we do not know what it consists of. Dark matter particles in the dark halo of our galaxy are being searched for in many ways. Indirect searches look for annihilation products and direct searches look for energy deposited within a detector. We will review several potential dark matter signals which have appeared in recent years both in direct and indirect searches. We will discuss in particular the data of PAMELA, ATIC, the Fermi Space Telescope and DAMA.
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