Physics and Astronomy Calendar

Week of Monday, November 19th 2018

Monday, November 19th 2018
12:15 pm:
Speaker: Soumyajit Mandal, Case Western Reserve University
Subject: Ultra-steep-spectrum Sources in Galaxy Clusters

Low-frequency radio observations have revealed the presence of large-scale synchrotron emitting sources in galaxy clusters. Over the last decade it has become clear that these sources trace particles (re-)accelerated by shocks and turbulence generated during major merger events. However, the physics of these particle acceleration processes is still poorly understood. One of the main open questions is the fate of fossil relativistic electrons deposited in the intra-cluster medium, e.g., the lobes and tails of cluster radio galaxies. Are these fossil electrons re-accelerated by merger-induced shocks and turbulence? And is there a link to the generation of giant radio halos and relics? We have carried out GMRT follow-up observations of a unique sample of diffuse, ultra-steep-spectrum radio sources in galaxy clusters selected from the GMRT 150-MHz sky survey (TGSS) and follow up LOFAR, Chandra observation is underway. By determining their detailed properties, we aim to establish the origin of these sources, as well as their connection to ICM particle re-acceleration processes. In this talk I will present our search and preliminary findings about this sample of radio phoenixes, which is likely the tip of the iceberg of a large population of fossil plasma sources.

Faculty Host: Thomas W. Jones

Tuesday, November 20th 2018
11:15 am:
Nuclear Physics Seminar in Physics 301-20 Tate
Speaker: Mauricio Martinez Guerrero, North Caroline State University
Subject: Hydrodynamic Fluctuations and Lower Bounds of the Transport Coefficients

In this talk I will discuss the effects of hydrodynamic
fluctuations in non-relativistic and relativistic setups. Within the
framework of stochastic hydrodynamics I obtain a number of model
independent results, including the long-time tail of different
transport coefficients, and the leading non-analyticity of the
correlators of energy, momentum and particle density in
non-relativistic and relativistic setups. The presence of hydrodynamic
fluctuations induce lower bounds on the transport coefficients by
analyzing the low frequency limit of different correlation functions.
I determine the lower bounds of the bulk viscosity over entropy ratio
in a cold Fermi gas near unitarity. When extending this analysis to
the case of a U(1) conformal relativistic expanding fluid we observe
that the values of the shear viscosity and heat conductivity are
bounded from below. In both setups, non-relativistic and relativistic
one, the lower bounds on the transport coefficients are weakly
dependent on assumptions regarding the range of applicability of fluid

1:25 pm:
Space Physics Seminar in Tate 301-20
Speaker: Aaron Breneman, University of Minnesota
Subject: Followup to Global-scale coherence modulation of radiation-belt electron loss from plasmaspheric hiss.
4:00 pm:
Speaker: Xiaoyu Wang, University of Chicago
Subject: Electrical transport near an Ising-nematic quantum critical point
Note change of time and day, this week only.

An electronic nematic order spontaneously breaks the rotation symmetry of the many body system, making various physical properties anisotropic. It has been observed in various systems, in particular the cuprate and iron-based high temperature superconductors. In the vicinity of a nematic quantum critical point — achieved by tuning some external parameter such as pressure or doping — the physics is described by that of low-frequency long-wavelength order parameter fluctuations coupled to a Fermi surface. However, due to the momentum-conserving nature of the induced electron-electron interaction, the temperature dependence of the resistivity near an Ising nematic QCP remains unclear. In this talk, we shed light on the problem by incorporating disorder and Umklapp process into the low-energy theory. Our work can be viewed as solving an extended Boltzmann equation, with a collision integral that accounts for complicated multi-particle scattering processes important near the QCP

Faculty Host: Rafael Fernandes

Wednesday, November 21st 2018
To be announced.

Thursday, November 22nd 2018
No journal club, Thanksgiving Holiday

Friday, November 23rd 2018
4:40 pm:
Thanksgiving - there will not be a speaker this week.

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