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This Week at Physics

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Events During the Week of October 9th through October 16th, 2011

Monday, October 10th, 2011

Plasma Physics (Physics/ECE/NE 922) Seminar
TBD
Time: 12:05 pm
Place: 2317 Engineering Hall
Speaker: James Hansen, Auburn University
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Condensed Matter Theory Group Seminar
Localization of quantum particles and classical waves in disordered media (Part I)
Time: 4:30 pm
Place: 5310 Chamberlin
Speaker: Peter Wölfle, Karlsruhe Institute of Technology, Germany
Abstract: In the first lecture I introduce the notion of localization in a random medium. The phenomenon of weak localization is discussed. In the regime of strong localization the concept of the metal-insulator Anderson transition is introduced. The statistics of the conductance in 1d and quasi-1d systems is presented. Then the fundamental concepts of the theory of Anderson localization are presented: scaling theory, renormalization group theory, symmetry classes, fractal structure of wave functions.
Host: Perkins
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Tuesday, October 11th, 2011

Chaos & Complex Systems Seminar
Recent changes in Wisconsin's forests as seen by satellites
Time: 12:05 pm
Place: 4274 Chamberlin
Speaker: Mutlu Ozdogan, UW Department of Forest and Wildlife Ecology
Abstract: Wisconsin's forests are changing rapidly as a result of commercial harvest, disease and climate. However, these changes are captured only at the county or at the national forest scales and thus are not suitable for local scale hydrological, biological, and climate studies. Using satellite observations spanning three decades, we are developing stand-level forest change maps at five-year intervals for northern Wisconsin. Our maps show that commercial forest harvesting is a major form of disturbance in northern forests and as a result, the size of contiguous intact forest blocks that are important for habitat and hydrological connectivity are diminishing. The seminar will walk the audience through some historical perspective on forest harvesting in Wisconsin, show the impact of satellite technology in mapping harvested blocks, and discuss the implications of forest change.
Host: Clint Sprott
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Theory Seminar (High Energy/Cosmology)
Signals of CP Violation Beyond the MSSM in Higgs and Flavor Physics
Time: 4:00 pm
Place: 5280 Chamberlin
Speaker: Stefania Gori, University of Chicago
Abstract: We study an extension of the Higgs sector of the Minimal Supersymmetric Standard Model (MSSM), considering the effects arising from new degrees of freedom at the TeV scale that are carrying new sources of CP violation beyond the MSSM. The new sources of CP violation have a strong impact on Higgs collider phenomenology and on low energy flavor and CP violating observables. Two striking Higgs benchmark scenarios are identified: a scenario with three neutral Higgs bosons that all decay dominantly into W boson pairs and a scenario with three relatively heavy Higgs bosons (~150 GeV) decaying dominantly into b bbar. We finally investigate the predictions of the model for those flavor observables that still allow the presence of sizable new physics effects while being compatible with the experiments. A particular emphasis is given to the rare decay Bs->mu mu and to the Bs mixing phase.
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Wednesday, October 12th, 2011

No events scheduled

Thursday, October 13th, 2011

R. G. Herb Condensed Matter Seminar
Pairing of critical Fermi-surface states
Time: 10:00 am
Place: 5310 Chamberlin
Speaker: Max Metlitski, Kavli Institute for Theoretical Physics, UC-Santa Barbara
Abstract: States of matter with a sharp Fermi-surface but no well-defined Landau quasiparticles are expected to arise in a number of physical systems. Examples include i) the spinon Fermi-surface (U(1) spin-liquid) state of a Mott insulator, ii) the Halperin-Lee-Read composite fermion liquid state of a half-filled Landau level and iii) quantum critical points associated with the onset of order in metals. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi-liquids to pairing. We show that for a large class of phase transitions in metals, the attractive interaction mediated by order parameter fluctuations always leads to a superconducting instability, which preempts the non-Fermi-liquid effects. On the other hand, the spinon Fermi-surface and the Halperin-Lee-Read states are stable against pairing for a sufficiently weak attractive short-range interaction. However, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between i) the U(1) and the Z2 spin-liquid states, and ii) the Halperin-Lee-Read and Moore-Read states.
Host: Chubukov
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Flavor symmetries and processes with tops
Time: 2:30 pm
Place: 4274 Chamberlin
Speaker: Jure Zupan, University of Cincinnati
Abstract: I will focus on two topics in top physics - the anomalously large forward backward asymmetry (A_FB) in t-tbar production and the newly suggested signal of dark matter production - single top with missing E_T. Large A_FB may be a sign of new physics, with new flavor symmetric sectors representing an attractive possibility. I will show which representations of SM global flavor group can lead to acceptable phenomenology. As for the second topic, I will show that a monotop signal may be the dominant signal of DM at LHC for a large set of models.
Host: Michael Ramsey-Musolf
Presentation: http://www.physics.wisc.edu/twap/presentations/2223.pdf
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Astronomy Colloquium
"Do Supermassive Black Holes Co-Evolve with Their Host Galaxies?"
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Chien Peng, Carnegie Observatories
Abstract: For almost 20 years, one of the intriguing puzzles in galaxy evolution is the strong correlations that have been observed between galaxies and their central supermassive black holes. The correlations suggested that galaxies and their central black holes somehow "knew" about each other, and that their evolution occurred in lock-steps. Theoretical models painted a beautiful picture that showed how quasar activity can both regulate the growth of the black hole and cause star formation inside galaxies to cease, thereby producing strong correlations that have been observed. The energy feedback by quasars in turn may solve a number of other puzzles in galaxy evolution. In recent years, new observations from quasars, ULIRGS, maser galaxies, and dwarf galaxies, are providing an increasingly complex picture about the relationship between black holes and galaxies. I will present recent data on the BH and galaxy relations both at high redshift and locally, evidence for a changing correlation, and controversies surrounding the observations. I will also discuss why, if black holes self-regulate galaxy growth as theories suggest, that self regulation should have happened before redshift 2, and subsequently the correlation may have to be maintained via statistical merging alone. However, I will explain how statistical merging may itself be able to explain the entire correlation, such that black holes and galaxies may actually not need to know about one another. Lastly, I will tie all the quasar data with observations of "red nugget," normal, galaxies at high redshift to illustrate which direction the needle compass points, despite there being controversies that remain about selection functions and black hole mass estimates in active galaxies.
Host: Professor Christi Tremonti
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Graduate Introductory Seminar
Neutrino and Dark Matter Physics Seminar
Time: 5:30 pm
Place: 2223 Chamberlin Hall
Speaker: Balantekin, Heeger, Maruyama
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Friday, October 14th, 2011

Cosmology Journal Club
An Informal discussion about a broad variety of arXiv papers related to Cosmology
Time: 12:00 pm
Place: 5242 Chamberlin Hall
Abstract: Please visit the following link for more details:
    http://cmb.physics.wisc.edu/journal/index.html
Please feel free to bring your lunch!
If you have questions or comments about this journal club, would like to propose a topic or volunteer to introduce a paper, please email Le Zhang (lzhang263@wisc.edu)
Host: Peter Timbie
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Physics Department Colloquium
Quantum Phase Transitions and Scale Invariance of Atomic Quantum Gases
Time: 3:30 pm
Place: 2241 Chamberlin Hall (coffee at 4:30 pm)
Speaker: Cheng Chin, University of Chicago
Abstract: Atoms at ultralow temperatures are fascinating quantum objects, which can tunnel through barriers, repel or attract each other, and interfere like electromagnetic waves. This wavy behavior of ultracold atoms evidently illustrates the particle-wave duality as discussed in quantum physics. By loading repulsively interacting atoms into tiny optical cells (or optical lattices), we show that the wavy nature of the atoms can be completely suppressed. At the same time, the gaseous sample develops an interesting multi-layer structure with density plateaus, resembling a multi-tier wedding cake. Our observation of the cake structure in 2D ultracold gases [1] raises new prospects to investigate the dynamics and transport across the phase boundary [2] and to identify universal scaling laws in the (quantum) critical regime [3]. Surprising findings along these directions will be presented and discussed.

References:
[1] In situ Observation of incompressible Mott-insulating domains in atomic gases Nathan Gemelke, Xibo Zhang, Chen-Lung Hung, Cheng Chin Nature 460, 995 (2009)
[2] Slow Mass Transport and Statistical Evolution of An Atomic Gas Across the Superfluid-Mott Insulator Transition Chen-Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin Phys. Rev. Lett. 104.160403 (2010)
[3] Observation of scale invariance and universality in two-dimensional Bose gases Chen-Lung Hung, Xibo Zhang, Nathan Gemelke, Cheng Chin Nature (2011) doi:10.1038/nature09722
Host: Saffman
Poster: http://www.physics.wisc.edu/twap/posters/2011/2187.pdf
Video: http://www.physics.wisc.edu/vod/2011/10/14.html
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"This Week at Physics" poster: http://www.physics.wisc.edu/twap/posters/2011/2011-10-10.pdf

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