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This Week at Physics

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Events on 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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