Events at Physics |
Events During the Week of November 1st through November 7th, 2009
Monday, November 2nd, 2009
- No events scheduled
Tuesday, November 3rd, 2009
- Chaos & Complex Systems Seminar
- Poetry, mathematics, and science
- Time: 12:05 pm
- Place: 5310 Chamberlin (Refreshments will be served)
- Speaker: Robin Chapman, UW Department of Communicative Disorders
- Abstract: I'll read poems of my own from Chaos seminar topics and from several recent anthologies that focus on the use of mathematics and science in poetry across the centuries, and then discuss briefly, and speculatively, what questions a science of poetry comprehension might ask.
- Astronomy Colloquium
- Can Quasars Quench Star Formation?
- Time: 3:45 pm - 5:00 pm
- Place: 3425 Sterling Hall
- Speaker: Christy Tremonti, UW Astronomy Dept
- Abstract: Since quasars were first recognized as cosmological sources their relation to galaxies has been a puzzle. We now know that quasars are powered by accretion of gas onto supermassive black holes at the centers of massive galaxies. What continues to elude our understanding is the impact that quasars have on their host galaxies. Recent numerical simulations suggest that quasars can drive powerful gas outflows that ultimately bring about an end to star formation and black hole activity. I will discuss observations designed to directly test this hypothesis. Because gas outflows are challenging to observe in the presence of a bright quasar, our study focuses on a sample of galaxies that are a few 100 million years past the peak of their star formation and black hole activity. In these 'post-starburst' galaxies we find evidence for outflowing cool gas with velocities upwards of 1000 km/s. We consider the energetics of the gas and argue that quasars play a significant role in removing gas from galaxies and quenching star formation.
- String Theory Seminar
- Toward a Holographic Model of Color Flavor Locking
- Time: 4:00 pm
- Place: 2301 Sterling Hall
- Speaker: Heng-Yu Chen, UW-Madison
- Host: Gary Shiu
Wednesday, November 4th, 2009
- No events scheduled
Thursday, November 5th, 2009
- R. G. Herb Condensed Matter Seminar
- Invariant form of spin-transfer switching condition
- Time: 10:00 am
- Place: 5310 Chamberlin
- Speaker: Yaroslaw Bazaliy, University of South Carolina
- Abstract: Spin-transfer torque is a result of a non-equilibrium magnetic interaction induced by a flow of electric current. In nano-size devices spin transfer is a mechanism for current-induced magnetic switching, an effect with many applications in computer memory and logic. Calculations of critical switching currents were performed analytically and numerically for many systems. However, a clear physical interpretation of the results was available only in special cases. We firstly derive an invariant form of the current-induced switching condition and show that there exists a figure of merit for the current ability to destabilize a minimum of magnetic energy and induce switching. The resulting approach based on the "switching ability" of the current provides an intuitive physical picture of the switching behavior in devices of any geometry. We secondly consider the problem of current-induced stabilization of the saddle points and show that it happens via a different mechanism due to the topological restrictions. Saddle points are normally stabilized by a current-induced merger with other equilibria. Finally, we present and emerging full picture of possible switching scenarios in spin torque devices.
- Host: Natalia Perkins
- NPAC (Nuclear/Particle/Astro/Cosmo) Forum
- The Baryon Resonance Spectrum and the 1/Nc Expansion
- Time: 4:00 pm
- Place: 5310 Chamberlin
- Speaker: Richard Lebed, Arizona State University
- Abstract: Why do baryon resonance multiplets exist, and what controls their formation and decays? It is natural to consider them as merely excited states of some three-quark or meson-nucleon potential. But these are just simplistic quantum-mechanical pictures that recognize neither the full field-theoretical complexities of QCD nor the extremely brief lifetimes of resonances due to quark pair production. Both of these issues are addressed by the 1/Nc expansion of QCD, where Nc is the number of color charges. Constraints arising at large Nc on meson-baryon scattering amplitudes not only create linear relationships between them, thus linking distinct partial waves and their embedded resonances, but also restrict the possible resonant decay channels. I present strong experimental evidence in favor of this approach, describe the multiplet structure that it predicts, and show how to perform the analysis beyond the strict large Nc limit by incorporating 1/Nc-suppressed effects. This program has been developed to the point that now one possesses a full effective field theory formalism for physics in the baryon resonance region.
- Host: Michael Ramsey-Musolf
- Introductory Graduate Seminar
- Astrophysics II: Astroparticle Physics and Neutrinos
- Time: 5:30 pm
- Place: 2223 Chamberlin Hall
- Speaker: Faculty, University of Wisconsin Department of Physics
- Abstract: Balantekin, Barger, Chung, Halzen, Heeger, Karle, McCammon, Montaruli, Ogelman, Ramsey-Musolf, Timbie, Westerhoff, Zweibel
Friday, November 6th, 2009
- Theory/Phenomenology Seminar
- Rapidity Gap Events in Squark Pair Production at the LHC
- Time: 2:30 pm
- Place: 2301 Sterling Hall
- Speaker: Sascha Bornhauser, University of New Mexico
- Host: V. Barger
- Physics Department Colloquium
- Precision Muon Physics: Capturing a Moment in a Lifetime
- Time: 4:00 pm
- Place: 2241 Chamberlin Hall (coffee at 3:30 pm)
- Speaker: David Hertzog, University of Illinois at Urbana-Champaign
- Abstract: Low-energy, precision measurements are important to establish the parameters of the Standard Model and to test various predictions in the quest for new physics signatures. I will discuss two of our experiments that recently reported first physics results. Both involve the muon lifetime, leading to the Fermi Constant at a new level of precision and the nucleon weak pseudoscalar coupling constant g_P, determined in an unambiguous manner for the first time. Future plans include a Fermilab-based next-generation muon anomalous magnetic moment measurement, which follows on the our effort that has provided one of the strongest hints of physics beyond the Standard Model today.
- Host: Heeger