College of Arts and Sciences

The detailed study of cosmic microwave background anisotropies has contributed to transform cosmology into a quantitative, data driven field. Techniques such as weak gravitational lensing and baryonic acoustic oscillations have the potential to become new powerhouses of precision cosmology over the next decade, taking cosmology into a new era of exciting discoveries. In this talk I will review recent developments towards the achievement of precision cosmology and present the current cosmological concordance model. I will discuss outstanding challenges and future avenues of investigation, and I will survey the evolution of the field in the next 25 years.

Continue reading… Precision cosmology for the 21st century – Roberto Trotta

The production and distribution of new isotopes is a key topic of the astrophysical theme of chemical evolution. We distinguish Galactic Chemical Evolution (GCE), which is concerned with abundances in stars and the Interstellar Medium (ISM), and Cosmic Chemical Evolution (CCE), which extends this research to galaxies, clusters of galaxies, and the Intergalactic Medium (IGM). The ultimate goal is to understand the origin and evolution of all known nuclei, their abundances in various environments, ranging from planetary- to stellar systems. The cosmic cycle is driven by the formation, evolution, and deaths of stars. Strong winds and explosive final stages of massive stars determine the chemical,

Continue reading… Astronomy with Radioactivities [joint colloquium with Astronomy] – Dieter Hartmann

For more than fifty years physicists have searched for a neutron Electric Dipole Moment (EDM) beginning with a search for Parity violation by Purcell and Ramsey. Today the search is motivated by a possible “large” violation of Charge-Parity (CP) symmetry which is suggested by the observation of substantially more matter than antimatter in the Universe. A new experiment is underway to search for a neutron EDM with the goal of improving the sensitivity by more than two orders-of-magnitude. This ambitious experiment brings together physicists with expertise in particle, nuclear, atomic and low-temperature physics. We will discuss the importance of searching for new sources of CP violation as well as the technical challenges involved in this new experiment.

Continue reading… A Neutron Electric Dipole Moment? – Brad Filippone

Under the action of external forces, thin sheets tend to bend out of plane rather than stretch. For weak forcing, this leads to the distinctive wrinkling instabilities that you see on your skin. When more strongly confined, sheets crumple, and condense stress into a network of ridges which confer rigidity on the bulk material. At even stronger forcing, ridges develop into plastic creases which lead to complex time-dependent mechanical properties. I will describe experiments that study various aspects of this progression of features, concentrating on the wrinkling patterns seen in ultra-thin polymeric sheets.

Continue reading… Wrinkling, Folding and Crumpling of Thin Sheets – Narayanan Menon

We will review a series of calculations and experiments that my research group has carried out over the past few years in which we have used picosecond and femtosecond laser pulses to image and manipulate electrons within an atom. The electrons can be excited into localized wave packets moving in orbits almost a micrometer in diameter. They approach the classical limit of a single atom. The electrons can also be manipulated into very complex shapes in which we are literally sculpting the or writing information upon it. The electrons can also be entangled and used for quantum information storage and processing.

Continue reading… Rydberg Electron Wave Packets: Observing and Manipulating Electrons within an Atom – Carlos Stroud

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.

Continue reading… The Quantum Mechanics of Global Warming – Brad Marston

We propose a model of carrier-mediated ferromagnetism in semiconductors that accounts for the temperature dependence of the carriers. The model permits analysis of the thermodynamic stability of competing magnetic states, opening the door to the construction of magnetic phase diagrams. As an example we analyze the stability of a possible reentrant ferromagnetic semiconductor, in which increasing temperature leads to an increased carrier density, such that the enhanced exchange coupling between magnetic impurities results in the onset of ferromagnetism as temperature is raised. We apply this approach to studying thermodynamic fluctuations of magnetization in small systems such as bound magnetic polarons and magnetic nano-islands.

Continue reading… Thermodynamics of carrier-mediated magnetism in semiconductors – A. G. Petukhov

Recent astronomical observations are forcing us to face the cosmological constant problem, which is perhaps the greatest challenge of modern fundamental physics. Solving it seems to require a paradigm shift in our thinking about nature. In this talk I will explain why the physics of the cosmological constant is so elusive, discuss the ideas oft seen in connection to it, and specifically review why changing the gravitational sector of the theory may help.

Continue reading… Out of Darkness: The Quest for Lambda – Nemanja Kaloper

The conventional view holds that girih (geometric star-and-polygon) patterns in medieval Islamic architecture were conceived by their designers as a network of zigzagging lines, and drafted directly with a straightedge and a compass. I discuss our recent findings that, by 1200 C.E., a conceptual breakthrough occurred in which girih patterns were reconceived as tessellations of a special set of equilateral polygons (girih tiles) decorated with lines. These girih tiles enabled the creation of increasingly complex periodic girih patterns, and by the 15th century, the tessellation approach was combined with self-similar transformations to construct nearly-perfect quasicrystalline patterns. Quasicrystal patterns have remarkable properties: they do not repeat periodically,

Continue reading… Quasicrystals in Medieval Islamic Architecture – Peter J. Lu

The revolution in low power microelectronics has enabled the development of electronically enabled golf clubs, radically changing the relationship between the golfer and the golf club. These intelligent sensor systems provide quantitative measurements of the golf swing with unprecedented detail. Additionally, they have been implemented to enable real-time, audio biofeedback on the motion of the club. Transforming the golf swing into an audio sound-space provides a novel perspective of the golf swing and has yielded new insight into many aspects of the swing, tempo and timing in particular. This talk summarizes some of the interesting physics and biomechanics that have been learned about the golf swing through the use of this technology.

Continue reading… When Obsessions Collide: Golf and Physics – Robert Grober

Cosmology has well and truly entered its ‘precision era’. The wealth of observations has led to ever tightening constraints on cosmological model parameters. Some of the most fundamental aspects of physics in the models however remain hidden behind the phenomenology of pseudo-parameters. Indeed many questions about how the early universe evolved remain unanswered. I will argue that, over the coming years, Cosmology will enter a ‘post-precision’ era where further observations will open a window onto the physics itself where many surprises may still be hiding.

Continue reading… Beyond Concordance Cosmology – C. Contaldi

The celebrated scaling theory of localization asserted that all two- dimensional (2D) Fermionic systems are insulators. However, experiments in the 1990’s have revealed an intriguing metallic state and metal-insulator transition in various 2D semiconductor systems, where the carriers are strongly correlated. It is still being debated that if this 2D metallic state is a new electronic state of matter stabilized by strong Coulomb interactions. We have studied electrical transport properties of strongly interacting 2D holes in the world’s cleanest Gallium Arsenide quantum well samples down to ultra-low temperatures (T ~ 0.01K). We found that removing the spin degree of freedom (by applying a magnetic field parallel to the 2D plane) gradually drives the system back to the conventional ‘Fermi liquid’

Continue reading… Metallic Behavior and the Metal-Insulator Transition in Strongly Correlated 2D Holes – Xuan Gao

Nematics are materials that have only orientation order, usually described by a non-zero, uniaxial average for a traceless symmetric second rank tensor. I review our knowledge about orientational order involving a single traceless symmetric second rank tensor order parameter or a single vector order parameter. There is recent interest in systems with either higher rank tensor order parameters or additional important, possibly higher rank orientational order parameters. I will discuss theoretical results for such generalized nematics, including the rather striking differences between systems with single low rank tensor and single high rank tensor order parameters. Such differences, which seem to be generic to high-rank tensor order parameters in various symmetry groups,

Continue reading… Generalized Nematics: Hints for the GUTS / Electroweak Transition? – Rolfe Petschek

Maxwell’s demon, which extracts work from a thermodynamic system by acquiring information about it, has for more than a century been a favorite thought-experiment in the foundations of statistical physics. The demon has variously been viewed as a threat, an exception, an exemplar, and a means for extending the Second Law. I will describe a formulation of thermodynamics in which such “information engines” play the central role, yielding insights about entropy, information erasure, the meaning of temperature, and the connection between fluctuation and dissipation.

Continue reading… Information Engines and the Second Law – Benjamin Schumacher

In this talk I will discuss the origins of magnetic exchange interactions in the underlying electronic structure from a first-principles point of view. I will start from the textbook examples of the Heisenberg Hamiltonian, the Stoner theory of itinerant magnetism and various indirect exchange couplings. I then pose the question of how these various behaviors should emerge naturally from a first-principles calculation of the electronic structure. I will present the disordered local moment picture that emerges from spin-density functional theory and how it is based on an adiabatic decoupling of slow and fast degrees of freedom. I will discuss how non-collinear magnetism and the linear response calculation of exchange interactions are naturally obtained in the framework of multiple scattering theories of electonic structure.

Continue reading… Magnetic exchange interactions – Walter Lambrecht

Clusters of galaxies emerge at dense peaks in the vast cosmic web of large-scale structure that threads the universe. The non-linear dynamics governing their formation has been extensively studied using computational N-body and gas dynamical techniques, and many population properties are now well understood (or, at least, well calibrated) from this first-principles approach. The links between cosmological parameters and cluster population statistics are now strong enough to motivate large observational programs at optical, sub-mm and X-ray wavelengths. In this talk, I will review progress in modeling clusters as multi-component, gravitational systems and then address the role that cluster studies should play in illuminating dark sector physics over the coming decades.

Continue reading… Computing the Cosmos: Illuminating the Dark Side with Clusters of Galaxies [joint colloquium with Astronomy] – Gus Evrard

Recent advances of magnetic resonance imaging (MRI) scanner design involve an ever-increasing number of receiver channels (32-128), which is required to realize the full potential of the so-called parallel imaging techniques that have been very rapidly developed over the last few years to improve the temporal and spatial resolution of MRI. In particular, 1.5-Tesla and 3-Tesla fast MRI clinical applications enabled by parallel imaging techniques are now realized and accepted as everyday routine clinical practices. At both of the field strengths, within the crucial constraints of maximum patient comfort and signal-to-noise ratio (SNR), the key requirement is an optimized multi-detector radiofrequency (RF) array coil leading to more advanced and faster clinical MR scans.

Continue reading… From Jackson Homework to Quality Electrodynamics – Hiroyuki Fujita

The world’s largest cosmic ray observatory has recently reported a new result that represents a major step forward in our understanding of the origins of the highest energy cosmic rays. The astrophysical origins of the highest energy cosmic rays have remained a persistent mystery for decades. Where in the universe do these particles come from? How do they obtain such enormous energies? Now, we seem to be on the verge of getting a new handle on these questions. The Pierre Auger Observatory, in Malargue, Argentina, has been operating since 2004, and already we have some clues, including the energy spectrum and limits on photon flux that strongly suggest an extragalactic origin for the highest energy cosmic rays.

Continue reading… Breaking News from the Auger Observatory – Corbin Covault

The cosmic microwave background (CMB) gives us a glimpse of the Universe as it was only a few hundred thousand years old. The tiny fluctuations — one part in 100,000 — that we observe in the CMB trace out the fluctuations that would eventually become the galaxies and clusters that we see today. Our theories, on the other hand, predict only the statistical properties of those initial conditions. Measuring cosmological parameters therefore requires disentangling those statistical properties from our finite, noisy observations. Today, those observations (from instruments like the COBE and WMAP satellites) tell us that the universe is geometrically flat,

Continue reading… The Cosmic Microwave Background: Cosmology, Topology and Probability – Andrew Jaffe

For a price, it is possible to acquire unearned academic degrees from non-existent universities that market diplomas over the internet. The most sophisticated of these diploma mill cartels, based in Spokane, Washington, is now the subject of a multi-agency criminal investigation. It has used the turmoil in Western Africa to foster the illusion of recognition and accreditation by the Republic of Liberia. But these credentials were obtained through payments to government officials, and are no more legitimate than the supporting web of fake diplomatic missions, schools, accreditors, and credential evaluators created by the “Saint Regis” group. Their operation spans at least eighteen states and twenty-two countries,

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Lyotropic chromonic liquid crystals (LCLCs) are formed by molecules with rigid polyaromatic cores and ionic groups at the periphery that form aggregates while in water [1]. Light scattering experiments demonstrate that the isotropic-to-nematic pretransitional behavior does not follow the classic Landau – de Gennes model, as the length of aggregates changes with temperature [2]. Most of the LCLCs are not toxic to the biological cells [3] and can be used as an amplifying medium in real-time biosensors [4]. The detector is based on the principle that the immune aggregates growing in the LCLC bulk trigger director distortions. Self-assembly of LCLC molecules into oriented structures allows one to use them in various structured films with potential applications as polarizers and optical compensators.

Continue reading… Chromonic Liquid Crystals – Oleg Lavrentovich

The use of thermonuclear supernova explosions as standard candles led to the discovery of cosmic acceleration and the search for the nature of dark energy. How good are these standard candles? How do we understand and model the variation in supernova properties? How does all of this fit in with what we know about stellar evolution and cosmic enrichment? I’ll describe what we know (and don’t know) about these questions and what is being done to answer them more securely in advance of a possible Joint Dark Energy Mission to measure the properties of dark energy.

Continue reading… Fundamentals of Supernova Cosmology [joint with Astronomy] – Robert P. Kirshner

Continue reading… Stabilizing Atmospheric CO_2 [joint colloquium with Chemistry] – Gregory H. Rau

Continue reading… Energy options [joint colloquium with Chemistry] – John Deutch

I will explore the similarities and differences between the process of writing science fiction and the process of “producing” science, specifically theoretical physics. What are the ground rules for introducing unproven new ideas in science fiction, and how do they differ from the corresponding rules in physics? How predictive is science fiction? (For that matter, how predictive is theoretical physics?) I will also contrast the way in which information is presented in science fiction, as opposed to its presentation in scientific papers, and I will examine the relative importance of ideas (as opposed to the importance of the way in which these ideas are presented).

Continue reading… Science And Science Fiction – Robert Scherrer

Photovoltaics (PV) technologies based on thin films of hydrogenated amorphous silicon (a-Si:H) and polycrystalline cadmium telluride (pc-CdTe) have met with considerable success over the past few years. These thin film PV devices are deposited by chemical and physical vapor deposition methods on low cost substrates. Optimized devices have become increasingly complex, and in the case of a-Si:H technology include as many as a dozen major layers and several minor layers, as well, designed to capture a broad range of the solar spectrum. In addition, post-deposition processing may be required, and in the case of pc-CdTe this includes a critical anneal under CdCl2 vapor.

Continue reading… Real-time polarization spectroscopies: applications in thin film growth and photovoltaics – Robert Collins

In quasi one dimensional systems, the flow of energy has many unusual features. In the first part of this talk, I will show that the heat conductivity diverges in the thermodynamic limit in a large class of such systems. The form of the divergence is shown analytically to be universal. In the second part, I will discuss how disorder makes the flow of energy very slow and creates problems with equilibration. In the third part, I will present numerical results for the non-equilibrium flow of energy in disordered one dimensional systems, leading to an exact identity for wave propagation in nonlinear media.

Continue reading… Energy Transport in One-dimensional Systems – Onuttom Narayan

A (mostly pictorial) history of how American physics evolved from Ben Franklin’s kite to the tens of billions of dollars spent annually in physics and physics-related research today.

Continue reading… The Physics Enterprise – C. Rosenblatt