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Events on Thursday, September 8th, 2022

Theory Seminar (High Energy/Cosmology)
Axion Solar Halos
Time: 12:00 pm
Place: Chamberlin 5280
Speaker: Joshua Eby, Tokyo U., IPMU
Abstract: Ultralight dark matter (ULDM) is known to form self-gravitating bound states through gravitational relaxation. There are intriguing hints in the literature suggesting similar dynamics might lead to overdensities in the solar system as well, with ULDM becoming bound to the Sun. These Solar Halos can be probed by experiments on Earth when their radius R > 1 AU, which implies ULDM particle masses m < 10^{-14} eV. For larger masses m, space-based missions on orbits within 1 AU can probe small, compact Solar Halos with exceptional reach; for scalar couplings probable in current and near-future atomic clock systems, the sensitivity can exceed that of Equivalence Principle tests and probe well-motivated space for natural scalar field models. I will review the state of the art on these topics, including the use of asteroids as direct probes of DM density, as well as several exciting NASA and international missions that motivate searches aboard space probes.
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NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Light at the end of the tunnel: Astrophysical searches for axion-like particles in gamma-ray energies
Time: 2:30 pm
Place: Chamberlin 4274
Speaker: Milena S. Crnogorcevic, University of Maryland
Abstract: Axion-like particles (ALPs) are a well-motivated candidate for constituting a significant fraction of dark matter. They are produced in high-energy environments, such as core-collapse supernovae (CCSNe), and could undergo conversion into gamma-rays in the presence of an external magnetic field, with a characteristic spectrum peaking in the 30--100-MeV energy range. CCSNe are often invoked as progenitors of ordinary long gamma-ray bursts (GRBs), allowing us to conduct a search for potential ALP spectral signatures using GRB observations with Fermi Large Area Telescope (LAT). In this presentation, I will talk about using the Fermi LAT's low-energy (LLE) technique which, in contrast to the standard LAT analysis, allows for a larger effective area for energies down to 30 MeV. I will summarize the statistical methods used in our analysis and the underlying physical assumptions, the feasibility of the upper limits on ALP coupling from our model comparison results, and an outlook on future MeV instruments in the context of ALP searches.
Host: Ke Fang
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