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Events on Thursday, February 9th, 2012

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
The Empirical Case For 10 GeV Dark Matter
Time: 2:30 pm
Place: 4274 Chamberlin Hall
Speaker: Dan Hooper, Fermilab / University of Chicago
Abstract: I will summarize and discuss the body of evidence which has accumulated in favor of dark matter in the form of approximately 10 GeV particles. This evidence includes the spectrum and angular distribution of gamma rays from the Galactic Center, the synchrotron emission from the Milky Way's radio filaments, the diffuse synchrotron emission from the Inner Galaxy (the "WMAP Haze") and low-energy signals from the direct detection experiments DAMA/LIBRA, CoGeNT and CRESST-II. This collection of observations can be explained by a relatively light dark matter particle with an annihilation cross section consistent with that predicted for a simple thermal relic (sigma v ~ 10^-26 cm^3/s) and with a distribution in the halo of the Milky Way consistent with that predicted from simulations. Astrophysical explanations for the gamma ray and synchrotron signals, in contrast, have not been successful in accommodating these observations. Similarly, the phase of the annual modulation observed by DAMA/LIBRA (and now supported by CoGeNT) is inconsistent with all known or postulated modulating backgrounds, but are in good agreement with expectations for dark matter scattering. This scenario is consistent with all existing indirect and collider constraints, as well as the constraints placed by CDMS. Consistency with xenon-based experiments can be achieved if the response of liquid xenon to very low-energy nuclear recoils is somewhat suppressed relative to previous evaluations, or if the dark matter possesses different couplings to protons and neutrons.
Host: Reina Maruyama
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Astronomy Colloquium
A New Look at Stellar Evolution: Chi-by-Eye Evolves to Bayesian Statistics
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Ted von Hippel, Embry-Riddle Aeronautical University
Abstract: In the 1960's stars were observed with single-channel photometers or worse, stellar evolution codes were run on a computer that barely bested a slide rule, and the results were compared by eye. While the observations and stellar models have improved tremendously in the interim, the methods by which we compare stellar models to data generally have not. I will describe a new Bayesian approach to this problem. Our Bayesian technique yields better precision in the ages, distances, etc. for stars and clusters, provides a fuller understanding of errors and correlations among the derived parameters, and allows us to attack a range of problems in stellar evolution in a consistent manner for the first time.
Host: Robert Mathieu, Chair of Astronomy
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Cosmic Accelerators: Pulsars and Pulsar Wind Nebulae
Time: 4:00 pm
Place: 4274 Chamberlin Hall
Speaker: Aous Abdo, George Mason University
Abstract: The rapid spins and intense magnetic fields (109 - 1014 Gauss) of pulsars accelerate particles to very high energies, both in their magnetospheres and in relativistic winds, powering emission from radio waves to the highest energy gamma-rays. NASA's Fermi Gamma-Ray Space Telescope, launched in 2008, has proved to be a powerful tool for studying these systems. Fermi observations have increased the population of known gamma-ray pulsars from 6 to more than 100. New classes of gamma-ray pulsars, including millisecond and radio-quiet pulsars, have emerged. With its unprecedented sensitivity, Fermi has transformed our understanding of the energetic particle accelerators in our Galaxy and thereby linked observations of the sky at the highest photon energies (1012 eV) with those at the lower end of the electromagnetic spectrum. In my talk I will discuss some of the new and exciting results from Fermi and focus on how these discoveries integrate with the overall picture of pulsars and their nebulae that covers some 20 decades of energy.
Host: Halzen
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