Physics and Astronomy Colloquia

Academic Year 2010-2011

Dept. of Physics & Astronomy, Stony Brook University


Colloquium committee: Meigan Aronson (spring chair), Axel Drees, Mike Marx, Hal Metcalf, Michael Zingale (fall chair)
Coffee & Tea served at 3:45 pm.
Talk begins at 4:15 pm.
Location: Harriman 137 (bottom of square C4 on the campus map)

 

Colloquia already given in academic year 2010/2011:


Fall 2010 colloquia

DateSpeakerTitleLocal Host
Sept. 7 Laura Baudis
Zurich
Direct Detection of Dark Matter in the Milky Way
We have strong evidence that about 95% of matter in our Universe is dark, revealing its presence only by its gravitational attraction. In hierarchical structure formation, two macro-structures exist in the Milky Way: the dark halo, and the dark disk. If the dark matter in these structures is made of Weakly Interacting Massive Particles (WIMPs), it can be directly detected via elastic scattering from nuclei in ultra-low background, deep underground detectors. WIMPs arise naturally in many beyond standard model theories, a popular example being the neutralino, or the lightest supersymmetric particle. After an introduction to the direct detection method, I will review the current techniques to search for these hypothetical particles. The focus will be on recent results, and on the most promising techniques for the near future.

[recorded movie]

Zingale
Sept. 14 Laszlo Mihaly
Stony Brook
Chair's Colloquium

[recorded movie]

Zingale
Sept. 21 Dmitri Tsybychev
Stony Brook
Searches for new sources of CP violation
CP violation is one of the three "Sakharov conditions" required to explain the baryon asymmetry of the universe. While CP violation is explained in Standard Model (SM) of particle physics and has been observed in decays of neutral kaons and B-mesons, but the level falls far short to explain the cosmic overabundance of matter. Thus physics "beyond" the Standard Model may be needed to explain the glaring discrepancy. In this talk we will present new results from Tevatron experiments that aim to find a deviation from SM prediction for CP violation and find its origin.

[recorded movie]

Zingale
Sept. 28 Webster Cash
Colorado
The New Worlds Observer: Direct Imaging and Spectroscopy of Earth-like Planets
The New Worlds Observer is a mission concept that can be realized in the coming decade. It features an Ultraviolet to Near-IR telescope of quality comparable to HST. A separate spacecraft, flying about 80,000km away along the line of sight to a nearby star carries a starshade that blots out the central star without decreasing the flux from exoplanets as close as .04 arcseconds. It will be possible to completely map hundreds of nearby planetary systems, identifying most of the major planets. It is expected that this will lead to the discovery of dozens of Earth-mass planets in the habitable zone. Immediate spectroscopy of the detected bodies will allow assessment of their true natures. The presence or absence of water lines and biomarkers will open the serious search for simple life in the Universe. Starshades can be used in combination with other telescopes, like JWST. A “New Worlds Technology Development Program” was just chosen as the top priority space activity in the medium cost class by the Astro2010 decadal panel.

[recorded movie]

Zingale
Oct. 5 John Hobbs
Stony Brook
Toward the Unknown: First Physics from Atlas
The Large Hadron Collider at CERN is now providing proton-proton collisions at the highest energies ever created in a laboratory. Initial results from the Atlas experiment including measurements of standard model processes and first searches for new particles will be shown. Prospects for the coming year and beyond will also be described.

[recorded movie]

Zingale
Oct. 12 Gordon Cates
Virigina
More spins, more resolution: Exploring the neutron and lungs using laser-polarized He-3
Laser polarized He-3 provides a powerful tool for both subatomic physics as well as medical imaging. Recent electron scattering measurements using a polarized he-3 target at JLab, in Newport News, Va, have provided what might loosely be called the highest resolution "snapshot" of the neutron to date through measurements of the electric form factor. In medical imaging, polarized He-3 has long provided the highest resolution images of the gas space of the lungs, work that has its origins in a Princeton/Stony Brook collaboration from the mid 1990's. Now He-3 can be used to provide high-resolution dynamic studies of lung function, as well as regional mapping of microscopic changes in lung structure. The next generation of studies in both subatomic physics and medical imaging continue to provide the potential for exciting new directions.

[recorded movie]

Metcalf
Oct. 19 Ilan Ben-Zvi
BNL
Cool beams for hot accelerators
Accelerator physics is a science in its own right and a driver for discovery science and a host of applications. I will describe a particular aspect of accelerator physics, that of high-brightness particle beams and how they lead to cutting edge accelerators. The presentation will be done mostly from a personal point of view with collaborative Brookhaven Lab and Stony Brook R&D and projects as the background.

[recorded movie]

Marx
Oct. 26 Ray Jayawardhana
Toronto
Characterizing Exoplanets
On-going searches for extrasolar planets, despite certain limitations in sensitivity, have already revealed a remarkable diversity of worlds --from close-in super-Earths to far out super-Jupiters-- and challenged our preconceptions many times over. Meanwhile, comparative studies of exoplanet physical properties have begun in earnest: planets caught in transit and those imaged directly are best suited for detailed characterization, especially of their atmospheres. I will discuss recent results and future prospects, including the possibility of extending these techniques to lower-mass planets.

[recorded movie]

Zingale
Nov. 2 Hal Metcalf
Stony Brook
A Subjective History of Laser Cooling
Optical forces, or light pressure, was derived by Maxwell and survived intact through both relativity and quantum optics simply because E = pc. It was studied in the 1908 Ph.D. thesis of Peter Debye on comet tails. The optical forces used for laser cooling require rather special properties, namely, velocity dependence so that when atoms are slowed to some selectable speed the force vanishes instead of reversing their direction and accelerating them again. This velocity dependence is often implemented through the Doppler shift: the light is tuned so that atoms would need to be Doppler-shifted into resonance with it. Atoms at rest would be too far out of resonance to interact strongly. Since this is the year of LaserFest, it's important to discuss why such cooling forces need to use laser light. The temporal coherence of laser light enables precise enough tuning and stability to control Doppler shifts on the scale of the natural width γ.

My role in laser cooling began in the late 1970's in a conversation with Bill Phillips while he was still a graduate student at MIT. When he explained the ideas to me, I responded that it simply couldn't work because shining laser light on something can only add energy and heat it up. I thought that was the end of it until it occurred to me that making ice cubes requires the refrigerator to be plugged in, and that its mechanism only served to redistribute heat energy. We need to think about laser cooling in terms of momentum (force), energy, and thermodynamics (entropy).

[recorded movie]

Zingale
Nov. 9 Dominik Schneble
Stony Brook
More Than a Sum of Parts: Ultracold Atomic Mixtures in Optical Lattices
Quantum gases in optical lattices allow for fundamental studies in atomic and condensed-matter physics, including strongly-correlated many-body systems. My talk will focus on possibilities with atomic mixtures (derived from a Bose-Einstein condensate) in lattices whose depth can be independently controlled for each component. In three recent experiments, we have explored novel features arising from interactions in the mixture: collinear atomic four-wave mixing, polaronic shifts in the strongly correlated regime, and scattering from crystalline atomic structures. My talk will conclude with prospects for future activities.

[recorded movie]

Metcalf
Nov. 16 R. Paul Drake
Michigan
High-energy-density physics of relevance to astrophysics
Our research program at the University of Michigan is focused on fundamental research in high-energy-density physics – seeking to understand the exotic behavior of dense collections of electrons, ions, and photons. The specific problems we choose are aimed at learning things in the laboratory that apply to astrophysics.

This talk will begin with an overview of high-energy-density physics, the study of systems at pressures near or above a million atmospheres, making them dense enough or hot enough to be ionized but too dense and/or too hot to behave as ideal plasmas do. In various regimes, quantum effects, relativistic effects, or electromagnetic effects are essential to understanding how such systems behave. These various regimes are in turn relevant to astrophysical systems where the same physical processes dominate the behavior.

The talk will then focus in more detail on our current work in high-energy-density hydrodynamics and radiation hydrodynamics. Our studies of the Kelvin Helmholtz and Rayleigh Taylor instabilities are motivated by mysteries in understanding mass transport in supernovae and by the limited range of scales that can be simulated with computers. We have seen effects that may relate to unknown features of the equation of state of highenergy- density matter and to the generation of magnetic fields. Our radiative shock studies are motivated by emerging observations of shock breakout from supernovae and by the need for experimental benchmarks for astrophysical codes with radiation. Having developed an experimental system in which radiative shock waves can be studied, we are proceeding to understand them more fully through a combination of new experiments, new diagnostic techniques, computer simulations, and theory. Our ongoing experiments at the National Ignition Facility seek to combine both these lines of research, by producing a hydrodynamic instability amidst a radiative shock, which further alters the hydrodynamic behavior.

* Supported by the US DOE NNSA under the Predictive Sci. Academic Alliance Program by grant DE-FC52-08NA28616, the Stewardship Sci. Academic Alliances program by grant DE-FG52-04NA00064, and the National Laser User Facility by grant DE-FG03-00SF22021.

[recorded movie]

Zingale
Nov. 23 no colloquium—classes on a Thurs. schedule
Nov. 30 Elizabeth McCormack
Bryn Mawr
Probing Long-Range Configurations of Molecular Hydrogen
Very long-range molecular configurations are of interest in a variety of contexts, for example, the astro-chemistry of cold molecular clouds and in planetary atmospheres, including our own. Such states can be more than 10 times the size of the ground state and often possess energies above multiple ionization potentials and dissociation limits resulting in diverse and complex decay dynamics. Many of these configurations possess a double-well character arising from the interaction of molecular Rydberg states and repulsive doubly-excited states at short internuclear distance, i.e., where molecular electronic configurations dominate, and between covalent and ionic states at larger internuclear distance, where electronic states are more atom-like. Of particular interest to us is that in the outer wells of the diatomic H2 system considerable ion-pair character can be present. The ion pair, an unusual molecular configuration consisting of one proton shrouded in a cloud of two electrons separated very far from the other proton, behaves very distinctly and is notoriously difficult to create in the laboratory. We will report on our investigation of lon-range states using resonantly enhanced multi-photon ionization via the state to probe the H(n=1) + H(n=3) dissociation threshold energy region. Both molecular and atomic ion production were detected as a function of wavelength by using a time-of-flight mass spectrometer. Below threshold a series of highly excited vibrational levels of the and Dstates of molecular hydrogen are observed. Term energies of multiple rovibrational levels the and D states and lifetimes of the J = 1-4, v = 12, 13 and 14 levels of the Dstate have been measured. For the D state, the observed trend of lifetime with vibration is strongly suggestive of a new dissociation channel opening up for the high vibrational levels. Above threshold broad resonances are observed with energies that agree well with the predictions of the mass-scaled Rydberg formula for bound states of the H+ H- ion pair. Ion-pair states with principal quantum numbers in the range of n ~ 130 to 210 have been observed. Our new results are comparable to recent experimental work using a different excitation scheme, which constituted the very first direct spectroscopic observation of heavy so-called Rydberg states in the H+ H- system.

[recorded movie]

Metcalf
Dec. 7 Arthur Eisenkraft
U. Massachusetts at Boston
A Colloquium in Memory of Clifford Swartz

Physics for All: From Special Needs to Olympiads
Can all students learn real physics? Physics First and Physics for All have become a success story for thousands of students in urban, suburban, and rural districts. At the same time, the International Physics Olympiad and other competitions have raised the expectation of what the most motivated students can achieve. Many physics educators are exploring ways to set higher goals for our most gifted students while also providing physics instruction to students previously excluded from our physics classes. Great novels and symphonies are accessible to people of different backgrounds and levels of expertise. We should develop teaching strategies that enable us to share an understanding of physics with all students because everyone deserves an opportunity to reflect on the wondrous workings of our universe.

[recorded movie]

Mihaly

 

Spring 2011 colloquia

DateSpeakerTitleLocal Host
Feb. 1 Ila Fiete
Texas
Neural codes for spatial location, velocity integration, and near-exact error correction
The brain represents and transforms external variables to perform computations. These processes are inherently noisy when performed by neurons. In recursive computations, such noise would accrue and could lead to catastrophic error, in contrast to what is seen behaviorally. The standard picture of how the brain might extract a less noisy estimate of the encoded variable is by averaging over large neural populations. Such population coding approaches lead to only modest (polynomial, or ~N) improvements in inverse squared error with increasing neuron number (N).

Is there a better way?

I will describe the peculiar encoding of 2-d animal location by so-called grid cells of the entorhinal cortex: individual cells fire at every vertex of a regular triangular lattice that tiles the plane. I will show how such responses could arise in a network model of simple interacting neurons. Finally, I will explain how and why the code enables unprecedented error control (inverse squared error ~e^{aN} for some a>0), compared to known neural population codes.

[recorded movie]

Aronson
Feb. 8 Steven Gubser
Princeton
On the sometimes happy relationship between string theory and heavy ion physics
String theory calculations, in the framework of the gauge-string duality, have had some positive effect on the understanding of heavy ion collisions. Notable successes to date include a realistic prediction of the shear viscosity and a semi-quantitative understanding of heavy-quark drag. I will survey a selection of results from string theory, or inspired by string theory, including some examples with happy endings (shear viscosity and quark drag) as well as some with less happy outcomes to date (total multiplicity and the location of the critical endpoint).

[recorded movie]

Drees
Feb. 15 Tom Abel
Stanford
Simulating Galaxies: One Star at a Time
Recent algorithmic advances allow now to study radiation magneto-hydrodynamical aspects of galaxy formation. The effects of non-equilibrium chemistry, atomic and molecular radiative processes, stellar radiation feedback as well as magnetic fields are being studied and some of their contributions in shaping galaxies documented. I will highlight the particulars of how early primordial massive stars shape the first galaxies through their radiative and supernovae feedback and discuss the chemical feedback from them. These stars while starting the process of cosmological reionization are found to displace large amounts of gas from their host dark matter halos. Their potential black hole remnants are found to be poor accreters and consequently are shown to not be progenitors of later super massive black holes. I will also show results on how magnetic fields are amplified in the formation of disk galaxies and discuss simulations of galaxy formation with hundreds of millions of star particles and resolution elements.

[recorded movie]

Zingale
Feb. 22 Howard Schneider
Stony Brook
Why Communicating Science Matters
In survey after survey, most Americans say they are interested in science, value its contributions and respect scientists. But the surveys also show that many Americans do not understand or accept scientific evidence and conclusions in areas like evolution, climate change, vaccination or the risk of radiation, and view investment in basic research as misguided. Stony Brook has taken the lead in creating an innovative new program in training future and current scientists to communicate more effectively with the public, the press, funders and colleagues across disciplines. Already, more than 200 scientists and graduate students at SBU, Brookhaven Lab and Cold Spring Harbor have participated in the program—which includes workshops ranging from writing for the public to improvisational theater games directed by Alan Alda. Howie Schneider, the dean of the School of Journalism, will report on the results so far, plans to expand the program for all science graduate students and faculty, and discuss the contributions of contemporary physicists and astronomers in “breaking the communications barrier.”

[recorded movie]

Metcalf
Mar. 1 Michael Thoennessen
MSU
Expanding the Nuclear Horizon
100 years after Rutherford discovered the atomic nucleus the limits of what combinations of protons and neutrons can make up a nucleus are still only known for the lightest elements. Exploring the nuclear landscape and pushing towards the limits of nuclear existence is important for the understanding of the strong force and the element formation in the universe. Even the observation of only a few nuclei of a new species can already yield information for example on the evolution of the proton-neutron interaction as a function of isospin or the path of the rapid neutron capture process responsible for the synthesis of the heavy elements beyond iron.

After about 10 years of very little progress the rate of discovery of isotopes has increased tremendously during the last few years. In 2010 over 100 new isotopes were reported which is the largest number of isotopes discovered in any given year. This increase is primarily due to the beginning of the operation of the RIKEN Radioisotope Beam Factory and to the technical advances to separate and identify heavy neutron-rich isotopes following uranium fragmentation at GSI. The new projects at GSI (FAIR) and MSU (FRIB) promise to expand the nuclear horizon even further.

[recorded movie]

Drees
Mar. 8 Steve Dierker
BNL
NSLS-II: Status, Plans, and Opportunities
NSLS-II is a planned new state-of-the-art, medium-energy storage ring designed to deliver ultra-high brightness and flux with top-off operation for constant output. It will operate at 3 GeV with a current of 500 mA, and includes novel design features such as explicit incorporation of damping wigglers and soft bend magnets to achieve ultra-low emittance. It will accommodate at least 58 beamlines and cover a very broad spectral range from the far-IR through the UV, soft x-ray, and hard x-ray ranges. It is currently under construction at BNL and scheduled to start operations in 2014.

The advanced capabilities of NSLS-II will have broad impact on a wide range of disciplines and scientific initiatives in the coming decades, including a wide range of nanometer-resolution probes for nanoscience, coherent imaging of the structure and dynamics of disordered materials, increased applicability of inelastic x-ray scattering, properties of materials under extreme conditions, and new studies of small crystals in structural biology.

The current status of the facility, the future plans, and the scientific opportunities will be discussed.

[recorded movie]

Aronson
Mar. 15 Gabriel Kotliar
Rutgers
Strongly Correlated Electron Materials: Some Dynamical Mean Field Theory (DMFT) Concepts and Applications
The aim of materials theory is to understand materials so that new substances with desired properties can be created. The development of quantum mechanics ideas and density functional theory based computational methods, has been extremely successful in this regard. In the twentieth century, a standard model of solids has been established, and it provides qualitative and quantitative guidance in the field of material research.

Correlated electron systems are outliers whose behavior do not fit within the standard model. They display remarkable phenomena ranging from metal to insulator transitions and high temperature superconductivity to anomalous thermoelectricity and volume collapses. They continue to surprise us with their exceptional physical properties and the perspectives for new potential applications.

The discovery of interesting strongly correlated compounds so far has been the result of serendipity and the application of the Edisonian approach, the most recent example provided by iron arsenide superconductors. From a theoretical perspective correlated electron systems are close to a localization-delocalization boundary. In this regime neither band theory (itinerant picture) nor atomic physics (localized picture) describes the physical properties of the materials posing one of the most difficult non-perturbative problems in physics

In the past two decades we achieved significant progress in the description of the electronic structure of correlated materials through the development of the dynamical mean field theory (DMFT) approach. In this lecture we will give an elementary introduction to the field of strongly correlated electron systems and to the ideas of Dynamical Mean Field Theory (DMFT). We will illustrate the methodology with examples drawn from f and d electron systems and conclude with an outlook of the challenges ahead and the prospective for theory assisted material design.

[recorded movie]

Aronson
Mar. 22 Angela Kelly
Lehman College, CUNY
Physics in Secondary Schools: Research on Factors Impacting Accessibility
High school physics is a gateway course for post-secondary study in STEM related fields, and an important component in the formation of students’ scientific literacy. Although the percentage of students taking high school physics has increased in recent years to a high of 37% in 2009 (AIP, 2010), access and enrollment have been unevenly distributed and have been influenced by a variety of factors. The presentation will focus on three aspects of physics accessibility in secondary schools: 1) quantitative data illustrating the status of physics availability in the U.S., New York State, and New York City, 2) qualitative data outlining the impacts of standardized testing on physics course-taking in several states, and 3) the unintended consequences of select districtand state-based reform initiatives on physics access and enrollment.

First, the limitations of urban secondary physics programs will be discussed through data collected in New York City, where physics course offerings have been limited and certain organizational variables have correlated to whether schools offer physics. Secondly, standardized testing content (Regents, FCAT, PSAE, etc.) has often marginalized physics in the secondary science sequence. Finally, teachers and administrators have shared their views of recent reform initiatives in their districts. I will present data from interviews and focus groups where key players have reflected on various reform structures and how they have been implemented and evaluated. Such policies have also influenced whether physics has been offered, and whether students have elected to take it. Future research related to student participation in physics will also be discussed.

[recorded movie]

Mihaly
Mar. 29 Zein-Eddine Meziani
Temple U
Nucleon Spin Structure and Quantum Chromodynamics
Nucleon spin structure studies at Jefferson Lab and their natural extension in the era of the 12 GeV energy upgrade as well as a future electron ion collider will be presented. Scattering experiments using a polarized electron beam and polarized targets at high luminosity have provided a wealth of data on the nucleon electromagnetic and spin structure with surprises and puzzles. These studies have helped us unravel the rich structure of the building blocks of matter and have impacted our understanding of QCD. A promising future is still ahead in the quest to complete our picture of nucleon structure and our grasp of QCD.

[recorded movie]

Drees
Apr. 5 Craig Fennie
Cornell
Multifunctional multiferroic oxides by design
The discovery of materials displaying novel properties is the driving force behind continued scientific progress across many disciplines. Due to their highly tunable ground states, structurally and chemically complex oxides are a promising class of materials in which to realize new emergent phenomena that could not only challenge our current understanding of condensed matter but also provide real solutions for technological advances in for example the energy sciences and electronics. The traditional exploratory route to identify new phenomena, however, is quite demanding, as there are an enormous number of possible materials that have yet to be identified. Additionally, recent advances in synthesis techniques facilitate tailoring and enhancing the properties of complex materials at the atomic scale, greatly extending the design variables.

In this talk I will discuss examples of our theory-driven experimental pursuit for new complex oxide materials rarely found in nature – ferromagnetic-ferroelectric oxides in which a spontaneous magnetism not only coexists with but also is strongly coupled to a spontaneous electric polarization. Additionally I will discus our most recent theoretical work in which we show how oxygen octahedron rotations, ubiquitous in perovskites and related materials, enable an electric field to globally and deterministically switch the magnetization 180, a challenge that so far has not been realized in a multiferroic. The most surprising result of this study may be that the specific materials already exist in nature. I will argue that contrary to its historic role, theory should be the first step in the discovery of new phenomena as it provides a natural starting point and roadmap for synthesis of truly unprecedented materials.

[recorded movie]

Dawber/Aronson
Apr. 12 Michael Zingale
Stony Brook
Meeting the Computational Demands of Astrophysical Convection
Many astrophysical environments are characterized by periods of low Mach number convective flow. For Type Ia supernovae (SNe Ia), the final explosion is preceded by centuries of slow convective burning that ultimately determines how and where the flames that burn through the white dwarf first ignite. Understanding this convective behavior is critical to modeling these explosive events. Similarly, in X-ray bursts, the convective burning in the accreted layer on a neutron star can influence the nucleosynthetic yields and whether any of the ash is observable.

Studying these systems requires algorithms that can model the flow for long timescales. Traditional compressible hydrodynamics algorithms must follow the propagation of soundwaves, even if they do not contribute to the dynamics. This results in a restrictively small timestep, making long timescale evolution infeasible. To make progress in modeling these events, we've developed a new low Mach number hydrodynamics code, Maestro. By filtering out the soundwaves, Maestro takes timesteps based on the fluid velocity, not the sound speed, allowing simulations to cover much longer timescales, and giving an enormous efficiency boost.

In this talk, I will present our results studying the convective phase in SNe Ia. Our full-star, three-dimensional simulations show that the ignition of the explosion that burns through the white dwarf is likely to be off-center. I will discuss the details of the ignition process and the implications for SNe Ia explosion models.

[recorded movie]

Apr. 19 no colloquium—Spring Break
Apr. 26 Geralyn Zeller
Fermilab
New Revelations in Neutrino Scattering
The MiniBooNE experiment at Fermilab has amassed the world's largest sample of neutrino and antineutrino events in the 1 GeV energy range; a sample that includes both quasi-elastic scattering and single pion production processes. Although the primary motivation for MiniBooNE has been the now-reported search for muon neutrino to electron neutrino oscillations, there has been recent regained interest in neutrino interaction physics. Such low energy neutrino cross section measurements have not been updated for decades, having been first measured in bubble and spark chamber experiments. New measurements are sorely needed and yield important constraints for neutrino oscillation experiments operating in this 1 GeV energy range. With an order of magnitude larger statistics than historically available, study of the MiniBooNE events is already providing new and unexpected insight into low energy neutrino scattering on nuclei. In addition to discussing these new MiniBooNE results, projections for future measurements will also be presented.

[recorded movie]

Marx/McGrew
May 3 Mei Bai
BNL
Spin Manipulation of Polarized Beams
Various physics experiments involving polarized beams require delicate spin manipulations. This ranges from Siberian snakes for avoiding depolarizing resonances, to spin rotators for directing the spin vector to the desired direction, to RF spin rotators for reversing spin direction and etc. This presentation reviews current spin manipulation techniques and their applications.
Drees
May 10 Graduate Advisor
Stony Brook
Graduate Awards Colloquium