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This Week at Physics

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Events on Thursday, September 25th, 2014

R. G. Herb Condensed Matter Seminar
Entanglement in many body systems
Time: 10:00 am
Place: Chamberlin 5310
Speaker: Israel Klich, University of Virginia
Abstract: In this talk, I will review work on entanglement entropy in many body systems, it's scaling, relation to numerics and possible experimental checks. I will then describe some recent results on effective entanglement hamiltonians in conformal quantum field theories. In particular, I will show how the free fermion entanglement Hamiltonian in 1d can be obtained by solving a Riemann-Hilbert problem and how finite size corrections to the Hamiltonian may be obtained by perturbing around the Riemann-Hilbert solutions, as well as explore subtle difference between the Neveu-Schwartz and Ramond sectors of free fermion fields.
Host: Maxim Vavilov
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Astronomy Colloquium
SPECIAL TIME! 2:30 PM
Angular Momentum Transport via Internal Gravity Waves in Evolving Stars
Time: 2:30 pm
Place: 4421 Sterling Hall
Speaker: Jim Fuller, Caltech
Abstract: Recent asteroseismic advances have allowed for direct measurements of the internal rotation rates of many sub-giant and red giant stars. Unlike the nearly rigidly rotating Sun, these evolved stars contain radiative cores that spin much faster than their overlying convective envelopes, but much slower than they would in the absence of internal angular momentum transport. We investigate the role of internal gravity waves in angular momentum transport in evolving low mass stars. In agreement with previous results, we find that convectively excited gravity waves can prevent the development of strong differential rotation in the radiative cores of Sun-like stars. As stars evolve into sub-giants, however, low frequency gravity waves become strongly attenuated and cannot propagate below the hydrogen burning shell, allowing the spin of the core to decouple from the convective envelope. This decoupling occurs at the base of the sub-giant&lt;br&gt;branch when stars have surface temperatures of roughly 5500K. However, gravity waves can still spin down the upper radiative region, implying that the observed differential rotation is likely confined to the deep core near the hydrogen burning shell. The torque on the upper radiative region may also prevent the core from accreting high-angular momentum material and slow the rate of core spin-up. The observed spin-down of cores on the red giant branch cannot be totally attributed to gravity waves, but the waves may enhance shear within the radiative region and thus increase the efficacy of viscous/magnetic torques.
Host: Professor and Dept Chair, Ellen Zweibel
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
PeV neutrinos from right handed neutrino dark matter
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Ryosuke Sato, KEK
Abstract: The Standard Model of particle physics fails to explain the important
pieces in the standard cosmology, such as inflation, baryogenesis, and
dark matter of the Universe. We consider the possibility that the
sector to generate small neutrino masses is responsible for all of
them; the inflation is driven by the Higgs field to break B−L gauge
symmetry which provides the Majorana masses to the right-handed
neutrinos, and the reheating process by the decay of the B−L Higgs
boson supplies the second lightest right-handed neutrinos whose CP
violating decays produce B−L asymmetry, a la, leptogenesis. The
lightest right-handed neutrinos are also produced by the reheating
process, and remain today as the dark matter of the Universe. In the
minimal model of the inflaton potential, one can set the parameter of
the potential by the data from CMB observations. In such a scenario,
the mass of the dark matter particle is predicted to be of the order
of PeV. We find that the decay of the PeV right-handed neutrinos can
explain the high-energy neutrino flux observed at the IceCube
experiments if the lifetime is of the order of 10^28 s.
Host: Ran Lu
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