The existence of dark matter (DM) has been made robust through multiple orthogonal astrophysical probes, yet the microscopic properties of DM remain unknown. In particular, it is unclear whether DM interacts with itself and/or with the standard model (SM) non-gravitationally. Cold DM, a single, collision-less particle species with negligible primordial thermal dispersion is largely considered the “concordance” DM model in the astrophysical community. Yet, observations on dwarf scales suggest that DM might be self-interacting. In this seminar, I will discuss two possible models which give rise to DM self-interactions and a subset of their astrophysical implications: 1) the namesake model self-interacting DM (SIDM), in which DM interacts only with itself non-gravitationally, and 2) milli-charged DM (mDM), in which DM can couple non-gravitationally with itself and with the SM via long-range interactions. I will start by discussing hydrodynamic simulations demonstrating SIDM induced delay of super-massive black hole growth in Milky-Way mass galaxies. I will then present semi-analytic calculations that show streaming mDM can cause transverse EM Weibel plasma instabilities in galactic systems, such as in merging galaxies clusters.
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