Galactic and cosmological probes of dark matter self-interactions
ABSTRACT
Dark matter self-interactions can lead to number-changing processes that become especially important in regions of high dark matter density. In this talk, I will discuss how such reactions shape both the astrophysical distribution of dark matter and the observable signals they can produce. First, I will show that multi-particle number-changing interactions can significantly deplete dark matter spikes at galactic centers, particularly for the cross sections expected from thermal freeze-out, while semi-annihilation can preserve spike structure in many cases. I will then turn to the phenomenology of semi-annihilation as a source of boosted dark matter, focusing on fluxes generated in the Galactic Center and on their detectability in direct detection and neutrino experiments. Finally, I will present a cosmological extension of this picture, where semi-annihilation in the inhomogeneous early Universe produces a redshift-dependent boosted dark matter flux that can enhance experimental sensitivity by orders of magnitude. Together, these results show that number-changing dark matter dynamics can leave complementary imprints in astrophysical structure, direct searches, and neutrino-based observations, opening new opportunities to probe sub-GeV dark matter.
