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Building research ties across Texas: This meeting brings together researchers interested in topics at the intersection of theoretical particle physics, astrophysics, and cosmology. Participants from various institutions in Texas present and discuss the latest developments in their subfields, with the aim of fostering ideas and collaborations among faculty, postdocs, and graduate students. The host institution rotates from year to year to enable interactions with local experts in neighboring subfields.
Meeting Website:
https://sites.google.com/view/texas-tacos/upcoming-meeting
Kimberly Boddy (UT Austin)
James Dent (Sam Houston)
Andrew Long (Rice)
Joel Meyers (SMU)
Louis Strigari (TAMU)
Welcome remarks by Chris Johns-Krull, chair of the Physics and Astronomy Department.
With the 2019 Event Horizon Telescope (EHT) sub-mm observation of M87*, the first horizon-scale image in history, we are now in position to infer the physical properties of jet/accretion flow/black hole (JAB) systems through direct comparison of phenomenological models with the regions surrounding supermassive black holes. Using general relativistic magnetohydrodynamic (GRMHD) simulations of M87, we compare parametric models in which plasma imparts energy to synchrotron emitters via turbulent heating to those in which the emitters derive their energy directly from magnetic fields. Positrons are incorporated into the general relativistic ray tracer IPOLE to postprocess the GRMHD simulations-- showing stark differences in polarization signatures between standard and normal evolution (SANE) and magnetically arrested disk (MAD) accretion modes due to positron-mediated Faraday effects. MAD simulations with both types of emission model considered are concordant with EHT M87 linear and circular polarization constraints. The inclusion of electrons, positrons and protons in our radiative transfer pipeline thus provides a powerful probe of the composition and phenomenology of JAB systems. We then consider the role of positrons in the primordial plasma of the early Universe. From approximately 10ms to 10s after the Big Bang, relativistic positronium (electron-positron) plasma was a billion times more abundant than protons and neutrons. We consider GRMHD simulations in this unique environment, in which we model the accretion of positronium by primordial black holes. With the addition of rotation and the magnetorotational instability, we show how accreting primordial black holes could account for at least a percent-level contribution to the dark matter budget today, as well as the gamma ray background.