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Events on Thursday, November 2nd, 2023

R. G. Herb Condensed Matter Seminar
Theory of Pines' demon in multiband metals
Time: 10:00 am - 6:00 pm
Place: 5310 Chamberlin
Speaker: Edwin Huang, Notre Dame
Abstract: In 1956, David Pines predicted the existence of an acoustic plasmon, dubbed a "demon", in metals with multiple and sufficiently distinct charge carrier species. Despite extensive searches, demons have not been observed directly until recent momentum-resolved electron energy-loss spectroscopy (M-EELS) experiments on Sr2RuO4. Here, we discuss the theoretical conditions for the existence of demons as a stable collective excitation in multiband metals. We find, without any fitting or tuning of parameters, agreement between experimental M-EELS spectra and multi-orbital random phase approximation (RPA) calculations of the charge susceptibility. A decomposition of the calculation of the susceptibility into intra- and inter-band components provides direct evidence of the out-of-phase character of the demon. Our findings thus demonstrate the utility of numerical calculations for the microscopic interpretation of experimental spectroscopy. Nature 621, 66–70 (2023)
Host: Ilya Esterlis
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Looking inside the Earth with neutrinos
Time: 2:30 pm - 3:30 pm
Place: CH5310 /
Speaker: Sergio Palomares Ruiz, IFIC (CSIC - University of Valencia)
Abstract: Looking at the Earth's interior with neutrinos is a realistic possibility with current and future neutrino detectors, which is complementary to geophysics methods, but it is based purely on weak interactions. In this talk, I will give an overview of the two main approaches to perform Earth tomography with neutrinos: (i) neutrino absorption tomography, based on partial absorption of a neutrino flux as it propagates through the Earth (at energies about a few TeV) and (ii) neutrino oscillation tomography, based on coherent Earth matter effects on the neutrino oscillatory pattern (at energies below a few tens of GeV). I will first discuss (i) and present the first neutrino tomography of Earth using IceCube data. Then, I will discuss (ii) and, in particular, I will focus on supernova neutrinos with tens of MeV.
Host: Francis Halzen
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Astronomy Colloquium
Electromagnetic Transients in the Disks of Active Galactic Nuclei
Time: 3:30 pm - 4:30 pm
Place: 4421 Sterling Hall
Speaker: Rosalba Perna, Stony Brook University
Abstract: The disks of Active Galactic Nuclei (AGNs) have emerged as interesting
environments for the evolution of stars and the compact objects they leave
behind. The very high density of the medium, combined with torques from the
gas, yield evolutionary paths for main sequence stars which
differ from those in typical galaxies.
Well known transient phenomena such as long and short GRBs may have
a different-than-usual appearance when emerging from AGN disks, and
new astrophysical phenomena, such as the accretion induced collapse
of neutron stars to black holes, may be commonplace in AGN disks.
Host: Ke Zhang
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