Fall 2012/Spring 2013

Fall 2011



- September 1

- September 8	Dept. Welcoming Reception


- September 15	Prof. Krishna Rajagopal (MIT) Liquid Quark-Gluon Plasma: Opportunities and Challenges	Bal
	What was the universe like microseconds after the big bang? At very high temperatures, protons and neutrons fall apart --- the quarks that are ordinarily confined within them are freed. Until recently, matter at these temperatures was thought to be a tenuous gas-like plasma. Then, experiments at the Relativistic Heavy Ion Collider at Brookhaven started recreating little droplets of big bang matter. And, nature served up hot quark soup --- the stuff of the big bang turns out to be a liquid. This realization has allowed, even driven, physicists trying to predict further properties of hot quark soup to use calculations done via string theory. In this domain, string theory is answering questions posed by laboratory experiments. I will describe the opportunities and challenges for coming experiments at RHIC and the LHC, chief among them being seeing, and then understanding, how a liquid with no apparent particulate description emerges from quarks and gluons.

- September 22	Prof. Sharon Glotzer (UMichigan) Of Shape and Entropy: Packing and Assembling Polyhedra	Bowick
	The packing of shapes has interested humankind for millennia. We investigate the packing of hard, regular polyhedra using computer simulation and show that entropy alone can order them into unique structures both simple and unexpectedly complex. We focus in particular on the hard regular tetrahedron, which forms a dodecagonal quasicrystal at 50% packing fraction. Assemblies of tetrahedra can be compressed to packing densities much greater than that of spheres, and as high as 85.63%, the current world record. We also discuss the truncated tetrahedron, which forms a variety of thermodynamically stable atomic crystal isostructures, and discuss the role of entropy in stabilizing these phases. Relevant links and papers: Here is a link to a NY Times article written about the packing of tetrahedra and our work: http://www.nytimes.com/2010/01/05/science/05tetr.html# Here is a link to a new preprint: http://arxiv.org/abs/1109.1323 2 papers: Nature and Progress Article

- September 29



- October 6 Maxwell School Auditorium, 4 PM.	The Kameshwar C. Wali Lecture in the Sciences and Humanities & Syracuse Symposium Prof. Ian Shipsey (Purdue University) Bionic Hearing: the Science and the Experience	Schiff
	Cochlear implants are the first device to successfully restore neural function. They have instigated a popular but controversial revolution in the treatment of deafness, and they serve as a model for research in neuroscience and biomedical engineering. In this talk the physiology of natural hearing will be reviewed from the perspective of a physicist, and the function of cochlear implants will be described in the context of historical treatments, electrical engineering, psychophysics, clinical evaluation of efficacy and personal experience. The social implications of cochlear implantation and the future outlook for auditory prostheses will also be discussed. About the speaker: Ian Shipsey is a particle physicist, and a Professor of Physics at Purdue University. He has been profoundly deaf since 1989. Recently he heard the voice of his daughter for the first time, and his wife's voice for the first time in thirteen years thanks to a cochlear implant.

- October 13	Prof. Frans Saepen (SEAS, Harvard University) Defects and Deformation of Colloidal Crystals and Glasses Studied by Confocal Microscopy	Bowick
	Colloidal particles in suspension form liquid, crystalline and glassy phases similar to those formed by atoms. The structure of the phase that is formed depends on the nature of the colloids and their interactions (hard sphere, charged, functionalization of the surfaces, monodisperse or alloy) and especially the density. Since the particles are “fat” (~1µm) and “slow” (~0.1s), they can be individually tracked in space and time by confocal microscopy. Dense colloidal systems therefore serve as "analog computers" for the study of the complex dynamics of defects in crystals (stacking faults, dislocations, grain boundaries) and the fundamental mechanisms of the deformation of simple glasses.

- October 20	Prof. Ramesh Narayan (Harvard Center for Astrophysics) Astrophysical Black Holes	Balachandran
	Astrophysicists have discovered two varieties of black holes in the universe: stellar-mass black holes with masses in the range 5 to 20 solar masses, and supermassive black holes with masses in the range million to several billion solar masses. A number of interesting phenomena have been observed from these black holes, many of which are not yet understood. According to the general theory of relativity, each black hole is completely described with just two parameters, namely its mass and its spin. Thus, a black hole is the simplest macroscopic object in all of physics. Astrophysicists expect that most black hole observations can ultimately be understood in terms of the black hole mass and spin, though this goal is yet to be achieved.

- October 27	Prof. Sidney Redner (Boston University) Statistical Physics of Citations	Schwarz
	What are the statistical properties of citations to scientific articles? I discuss this question using recently available large-scale citation data .I will begin by presenting some amusing empirical facts about scientific citations from all citations of Physical Review publications from the past110 years. Intriguingly, the evolution of citations appears to be described by the mechanism of linear preferential attachment. I'll discuss the implications of linear preferential attachment on the properties of the citation network. Empirically, the citation distribution in the Physical Review appears to be described by a log-normal form, which does not accord well with linear preferential attachment. I will also discuss the use of the Google page-rank algorithm to find scientific "gems" in Physical Review---ground-breaking publications that are not so well cited. Finally, I will show how major scientific fields and connections can be uncovered by resolving the networks of citations into its constituent communities. web link: http://physics.bu.edu/~redner/pubs/pdf/PT.pdf

- November 3	Jeff Weeks (owner of "Geometry Games") Guided tour of finite spaces	Armendariz-Picon
	An elementary visual introduction to finite spaces, first in two dimensions and then in three, using physical models and computer animations. The theme throughout will be the tight connection between topology and geometry. Towards the end we'll take a brief look at how the cosmic microwave background hints that the real universe may be finite, and, if so, favors a "well proportioned" universe. The whole talk (except maybe the last 5 minutes) will be easily accessible to physics and math undergrads as well as to graduate students Web Link: www.geometrygames.org (see above)

- November 10	Prof. Glenn Starkman (Case Western) How the CMB Challenges Concordance Cosmology	Watson
	The Cosmic Microwave Background Radiation is our most important source of information about the early universe. Many of its features are in good agree- ment with the predictions of the so-called standard model of cosmology -- the Lambda Cold Dark Matter Inflationary Big Bang. However, the large- angle correlations in the microwave background exhibit several statistically significant anomalies compared to the predictions of the standard model. On the one hand, the lowest multipoles seem to be correlated not just with each other but with the geometry of the solar system. On the other hand, when we look at the part of the sky that we most trust – the part outside the ga- lactic plane, there is a dramatic lack of large angle correlations. So much so that no choice of angular powerspectrum can explain it if the alms are Gaus- sian random statistically isotropic variables of zero mean.

- November 17	Prof. Tomasz Skwarnicki (Syracuse University) Recent results from LHCb
	The LHCb experiment at CERN is devoted to searches for new types of interaction in decays of bottom and charm quarks. Substantial amounts of data have been accumulated this year. We present recent results from LHCb and discuss its future potential

- November 24	Thanksgiving Break


- December 1	Prof. David Merritt (RIT) Dynamics of Extreme-Mass-Ratio Inspirals	Armendariz-Picon
	Encounters between stars and stellar remnants at the centers of galaxies drive many important processes, including generation of gravitational waves via extreme-mass-ratio inspirals (EMRIs). The fact that these encounters take place near a supermassive black hole (SMBH) turns out to be important for two reasons: (1) The orbital motion is quasi-Keplerian, so that correlations are maintained for much longer than in purely random encounters. (2) Relativity affects the motion, through mechanisms like precession of the periapse, frame-dragging, and quadrupole torques. The interplay between these processes is just now beginning to be understood, based on N-body simulations that contain a post-Newtonian representation of relativistic dynamics. A key result is that relativity can be crucially important even for orbits that extend outward to a substantial fraction of the SMBH influence radius, by destroying the long-term correlations that would otherwise drive the evolution. I will discuss this work and its implications for the EMRI problem, for experimental tests of theories of gravity, and for the long-term evolution of galactic nuclei.

- December 8	Prof. Edo Berger (Harvard) Shake, Rattle, and Explode: Short GRBs and Gravitational Waves	Brown
	I will discuss the properties of short GRBs and our quest to decipher their properties with an ephasis on implications for gravitational wave detections.


	SPRING 2012

- January 19	Prof. Victor Yakovenko (University of Maryland, College Park) Statistical Mechanics of Money, Income, Wealth, and Energy Consumption	LaHaye
	By analogy with the probability distribution of energy in physics, I argue that the probability distribution of money in a closed economic system should follow the exponential Boltzmann-Gibbs law. Analysis of the empirical data shows that income distribution in the USA has a well-defined two-class structure. The majority of the population (about 97%) belongs to the lower class characterized by the exponential ("thermal") distribution. The upper class (about 3% of the population) is characterized by the Pareto power-law ("superthermal") distribution, and its share of the total income expands and contracts dramatically during bubbles and busts in financial markets. The probability distribution of energy consumption per capita around the world also follows the exponential Boltzmann-Gibbs law. Web links: http://physics.umd.edu/~yakovenk/econophysics/ http://physics.umd.edu/~yakovenk/econophysics/animation.html http://physics.umd.edu/~yakovenk/papers/RMP-81-1703-2009.pdf http://physics.umd.edu/~yakovenk/papers/2010-NJP-v12-n7-p075032.pdf

- January 26


- February 2	Prof. Paul McEuen (Cornell) Nano carbon: from solar cells to atomic drums	Plourde
	Graphene is the world’s first atomic membrane, a robust, one‐atom thick freestanding layer of sp2‐ bonded carbon. Graphene membranes are strong but highly flexible, with bending stiffness comparable to a lipid bilayer but stretching stiffness similar to diamond. Meter‐scale polycrystalline graphene films can now be produced cheaply and easily, opening the door to applications in both science and technology. Equally fascinating are carbon nanotubes ‐‐ nanometer‐diameter cylinders of graphene. These make great 1D transistors, diodes, and even nanoguitar strings. In this talk we will present new results on the structural, optoelectronic, and physical properties of nanotubes and graphene. Topics include the first STEM images of graphene grain boundaries and the patchwork‐quilt‐like structure of graphene grains. We also discuss experiments on graphene atomic drums that can be “played” either electrically or optically. Finally, we will present ultrafast measurements of photocurrent in both nanotube and graphene p‐n junctions. These experiments probe the fundamental excitation, relaxation, and transport processes that are key to applications ranging from graphene photodetectors to ultra‐efficient nanotube solar cells.

- February 9

- February 14 Tuesday	Dr. Linda Carpenter (University of California, Irvine) The Complete Abdridged Higgs Boson
	The Higgs Boson is believed to be the missing piece that completes the Standard Model of Particle Physics, solving many of the leading theoretical mysteries of the electro-weak scale. We expect a Higgs boson to be accessible to current experiments, and in fact the Large Hadron Collider may have already given us an important clue about its existence. In this talk I will employ both theoretical and experimental results to address the necessity of the Higgs Boson to the Standard Model, to discuss the status of Higgs physics as it stands now, after the first 7TeV run of LHC, and to explain how current Higgs searches are important tools for ruling on a variety of Beyond the Standard Model scenarios.

- February 16	Dr. John "Jack" Laiho (University of Glasgow) Flavor Physics and Lattice QCD
	An overview of recent Lattice Quantum Chromodynamics results will be given, and the impact on searches for new physics beyond the Standard Model of particle physics will be presented.

- February 23	Dr. Adam Martin (Fermi Lab) What if we don't find the Higgs?
	With the first full year of LHC running completed, we have a good idea where the Higgs boson isn't. There are excess events in the remaining allowed mass region, but those excesses may disappear with more data. What then? In this talk I will review the role the Higgs boson plays in the standard model and discuss how the theory can be adjusted to 'hide' the Higgs. These adjustments range from slight tweaks to the Higgs decay channels to removing the Higgs boson completely!

- February 28 Tuesday	Dr. Michael Endres (RIKEN, Japan) The unitary Fermi gas and other strongly coupled systems: from the perspective of the lattice
	Among the physicist's arsenal of tools for studying interesting physical phenomena theoretically is perturbation theory: an expansion in small dimensionless quantities about known and well-understood (albeit typically less interesting) solutions. Unfortunately, for a variety of strongly coupled systems, no such small parameters exist, rendering analytical calculations based upon perturbation theory unreliable. Such is the case for Quantum Chromodynamics (QCD), the theory of quarks and gluons, where at low energies the quarks combine to form protons, neutrons and more exotic hadronic states, and it is also the case for some more speculative theoretical descriptions of physics beyond the Standard Model as well. In this talk, I will explore how the lattice--and in particular how numerical simulations--can play an important role in achieving a quantitative understanding of nonperturbative physics in strongly interacting systems. I will describe the lattice technique from the point of view of a simple, yet surprisingly rich system known as the ``unitary Fermi gas''. Despite it's simplicity--or perhaps because of it--this dilute gas of strongly interacting fermions lies at the intersection of condensed matter, atomic, nuclear and particle physics, and offers a clear vantage point for the simple beauty and power of the lattice.

- March 1	Dr. JiJi Fan (Princeton University) Low-scale Supersymmetry: Where are we? Where are we going?
	The Large Hadron Collider (LHC) has been operating successfully for more than one year now and delivered a plethora of new results that start to change the landscape of particle physics. One of the key theoretical questions we hope LHC to shed light on is the nature of "hierarchy problem", that is, why electromagnetic and weak nuclear interactions are much stronger than the gravitational interaction. In this talk, I will explain in some detail the hierarchy problem and its key role in driving studies of new physics beyond the standard model for the last forty years. Supersymmetry has been one of the most compelling possible explanations for the hierarchy problem. However, LHC has excluded some of the most striking possible manifestations of supersymmetry. On the other hand, LHC has only started to probe the supersymmetric parameter region most relevant to solving the hierarchy problem. Besides, LHC has observed some exiciting evidence for a light Higgs boson with mass at around 125 GeV. If the observation holds up, it also has a profound implication for supersymmetric scenarios. I will discuss the current status of supersymmetry and the options for weak-scale supersymmetric theories in light of the LHC data from both supersymmetry searches and Higgs searches.

- March 8	Dr. Aleksey Cherman (University of Cambridge, UK) Approaching super-dense nuclear matter using large N methods
	An outstanding open challenge of theoretical particle and nuclear physics is understanding what happens to matter when it is squeezed to beyond nuclear densities, as is thought to happen in the interiors of neutron stars. The properties of matter at such densities are determined by QCD, and perturbative treatments of QCD are not reliable for the most interesting range of densities. The only reliable non-perturbative approach to studying QCD is through computer simulations, which use Monte Carlo methods to evaluate observables. Unfortunately, using these techniques for QCD at finite density has not been possible due to the infamous `fermion sign problem'. After reviewing some of the fascinating behavior expected from super-dense matter and explaining why the sign problem is a serious problem, I will explain a recent proposal to dodge the sign problem by exploiting properties of the limit of QCD where the number of quark colors becomes large.

- March 15	Spring Break


- March 22	Prof. Amir Caldeira (University of Campinas) Cats, decoherence and quantum measurement	LaHaye

- March 28

- March 29	Prof. Anatoly Kolomeisky (Rice University) Mechanisms of Formation of Signaling Molecules Concentration Profiles	Movileanu
	Concentration profiles of signaling molecules, also known as morphogen gradients, play a critical role in the development of multi-cellular organisms by determining polarity and spatial patterning that leads to further tissue differentiation. Large advances in studying morphogen gradients have been achieved recently when the formation of signaling molecules profiles has been visualized with high temporal and spatial resolution. A widely used approach to explain the establishment of concentration gradients assumes that signaling molecules are produced locally, then spread via a free diffusion and degraded uniformly. However, recent experiments have produced controversial observations concerning the feasibility of this theoretical description. In addition, latest theoretical analysis of times to establish the morphogen gradient yield surprising linear scaling as a function of length, not expected for the systems with unbiased diffusion process. We propose here a theoretical approach that provides a possible microscopic explanation of these observations. It is argued that relaxation times are mostly determined by first-passage times and the degradation effectively accelerates diffusion of signaling particles by removing slow moving molecules. Our theoretical analysis indicates that spatial and temporal features of degradation efficiently control the establishment of signaling molecules profiles.

- April 5	Prof. Fred Adams (University of Michigan Constraints on the Birth Environment of the Solar System
	Most stars -- and hence most solar systems -- form within groups and clusters. The first objective of this talk is to explore how these star forming environments affect solar systems forming within them. The discussion starts with the dynamical evolution of young clusters with N = 100 - 3000 members. We use N-body simulations to study how evolution depends on system size and initial conditions. Multiple realizations of equivalent cases are used to build up a robust statistical description of these systems, e.g., distributions of closest approaches and radial locations. These results provide a framework from which to assess the effects of clusters on solar system formation. Distributions of radial positions are used in conjunction with UV luminosity distributions to estimate the radiation exposure of circumstellar disks. Photoevaporation models determine the efficacy of radiation in removing disk gas and compromising planet formation. The distributions of closest approaches are used in conjunction with scattering cross sections to determine probabilities for solar system disruption. The result of this work is a quantitative determination of the effects of clusters on forming solar systems. The second objective of this talk is to use these results to place constraints on the possible birth environments for our solar system. REFERENCE: This talk ties together a number of issues in astrophysics, including star formation, planet formation, and the place of our Sun in the universe. As such, it should be of interest to a general audience. I have recently written a review article on this topic for Annual Reviews of Astronomy and Astrophysics. This article should be accessible to graduate students and people working in other fields. Reference = F.C. Adams, 2010, Ann. Rev. Astron. Astrophys., 48, 47

- April 12	Prof. Dmitrii Makarov (Univ Texas Austin) Polymer physics perspective on unfolded proteins and DNA: A spherical cow or a viable theory?	Movileanu
	The nature of the unfolded state of proteins is essential for our understanding of how proteins fold or how intrinsically disordered proteins accomplish their biological function. Likewise, unfolded proteins and single-stranded DNA play an increasingly important role in many recent biosensing devices. Polymer theory predicts remarkably simple, universal scaling laws governing long disordered polymer chains, which hold regardless of structural or chemical details as long as the chains in question are long enough. Unfortunately, real biopolymers are typically relatively short and so many researchers justifiably view polymer scaling theory approach to unfolded biomolecules as studying a “spherical cow”. In this talk, I will describe some of our recent efforts to understand the dynamics of unfolded biopolymers (proteins and single-stranded DNA) through a combination of computer simulations, polymer theory, and analysis of experimental results from our colleagues. These efforts have led us to the somewhat unexpected conclusion that simple polymer-theoretical concepts that disregard sequence effects can often be used to quantitatively understand the dynamics of unfolded polymers. In addition, they have shed light on the physical origins of the fascinating but rather poorly understood phenomenon of internal friction.

- April 19	Prof. Patrick Meade (Stony Brook) The Standard Model and Beyond at the LHC
	In this talk I will give an overview of the possibilities for Beyond the Standard Model (BSM) physics that might be found at the LHC. I will present a rough guide to where we stand after one year of running at the LHC and what this implies for BSM physics currently and in the future.

- April 26	Prof. Aashish Clerk (McGill University) In Search of Quantum Quivering: Quantum Electromechanics & Optomechanics	LaHaye
	The last decade has seen a remarkable amount of progress in the study of quantum coherence and measurement in condensed matter systems; experimentalists now almost routinely prepare and probe quantum states of electronic circuits. Attention has recently focused on attempting to produce and perhaps exploit quantum effects in relatively large mechanical objects by coupling them to quantum electronic circuits, or to driven optical cavities. Not only does this work seek to test quantum mechanics in a previously untested regime of large masses, it also holds the promise of helping further our understanding of quantum dissipation and quantum measurement; applications to quantum information processing and ultra-sensitive force detection are also envisaged. In this talk, I will discuss some of the remarkable experimental progress in this field, and will highlight some related theoretical questions being pursued by my group. http://physics.aps.org/articles/v2/40