Events at Physics
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Events on Thursday, February 26th, 2015
- Astronomy Colloquium
- "Cosmic ray feedback in Galaxies and Cool Core Clusters"
- Time: 3:30 pm
- Place: 4421 Sterling Hall
- Speaker: CHristopher Pfrommer, HITS Heidelberg
- Abstract: Understanding the physics of galaxy formation is arguably among the greatest problems in modern astrophysics. Recent cosmological simulations have demonstrated that "feedback" by star formation, supernovae and active galactic nuclei appears to be critical in obtaining realistic disk galaxies, to slow down star formation to the small observed rates, to move gas and metals out of galaxies into the intergalactic medium, and to balance radiative cooling of the low-entropy gas at the centers of galaxy clusters. However the particular physical processes underlying this "feedback" still remain elusive. In particular, these simulations neglected cosmic rays and magnetic fields, which provide a comparable pressure support in comparison to turbulence in our Galaxy, and are known to couple dynamically and thermally to the gas. Using hydrodynamic simulations of galaxy formation, I will show how cosmic rays are able to drive powerful galactic winds in low-mass galaxies. This reduces the available amount of gas for star formation and implies a shallower slope of the faint-end of the galaxy luminosity function as required by observations. In the second part of the talk I demonstrate that cosmic-ray heating can balance radiative cooling of the low-entropy gas at the centers of galaxy clusters and helps in mitigating the star formation of the brightest cluster galaxies. New data on the low-frequency radio and gamma-ray emission of M87, the closest active galaxy interacting with the cooling cluster plasma, enable us to put forward a comprehensive, physics-based model of feedback by active galactic nuclei.
- Host: Prof Jay Gallagher and Chair Ellen Zweibel
- R. G. Herb Condensed Matter Seminar
- Faculty Candidate Seminar
- Many body localization: a new frontier for quantum statistical physics
- Time: 4:00 pm
- Place: 4274 Chamberlin Hall
- Speaker: Rahul Nandkishore, Princeton Center for Theoretical Science
- Abstract: The existing theory of quantum statistical mechanics describes open systems in contact with large reservoirs. However, experimental advances in the construction and control of isolated quantum systems have highlighted the need for an analogous theory of isolated quantum systems. It has been realized that isolated many body quantum systems can support behavior which has no analog in traditional statistical mechanics. A prominent example is the phenomenon of many body localization.
Many body localization occurs in isolated quantum systems, usually with strong disorder, and is marked by absence of dissipation, absence of thermal equilibration, and a memory of the initial conditions that survives in local observables for arbitrarily long times. The many body localized regime is a far from equilibrium, strongly disordered regime that constitutes a new frontier for quantum statistical mechanics. Recently, my co-workers and I have demonstrated that many body localization opens the door to new states of matter which cannot exist in thermal equilibrium, such as topologically ordered states without a bulk gap, and broken symmetry states at high energy densities in one dimension. We have also uncovered a host of unexpected properties, such as a set of universal spectral features and a non-local charge response, that have striking implications for fields as diverse as quantum Hall based quantum computation and quantum control. In this talk, I review the essential features of the many body localization phenomenon, and present some of the recent progress that has been made in this field. I also discuss the implications of these results for both theory and experiment, and the connections with diverse areas of theoretical physics. I conclude with a discussion of future directions.
Reference: Rahul Nandkishore and David A. Huse, arXiv: 1404.0686 [Annual Reviews of Condensed Matter Physics, 2015]
- Host: Coppersmith