The Effects of Plasma Instabilities Induced by Long-Range SIDM on Milky Way Subhalos

Abstract

While most studies of self-interacting dark matter (SIDM) focus on short-range interactions dominated by the hard scattering of particles, this thesis explores SIDM dominated by long-range interactions. Specifically, we investigate the implications of long-range interactions within the dark sector, focusing on a dark matter subhalo streaming through the Milky Way. We show that such interactions can give rise to collective phenomena analogous to plasma instabilities in the Standard Model. We characterize the linear growth of these instabilities in the presence of a streaming subhalo, and use particle-in-cell (PIC) simulations to study their non-linear evolution. Our results reveal that the instability induces mixing between the subhalo and the Milky Way background, leading to density fluctuations. These fluctuations could, in principle, perturb stellar orbits, motivating a search for kinematic signatures in ultra-faint dwarf galaxies to constrain this model. Additionally, we propose that the outer layers of the subhalo may undergo an evaporation-like process as a result of this mixing, resulting in a more compact object by the time the subhalo reaches the inner galaxy.