Beyond Collisionless Dark Matter: Particle Physics Dynamics for Dark Matter Halo Structure

TL;DR

This paper explores the complex velocity and angular dependence of dark matter self-interactions mediated by a light particle, providing new analytic tools and mapping the full parameter space relevant for cosmic structure formation.

Contribution

It introduces a method to analyze the velocity and angular dependence of dark matter self-scattering in complex regimes, extending beyond simple models.

Findings

Mapped the parameter space of dark matter self-interactions

Derived a new analytic formula for resonant s-wave scattering

Linked self-interactions to Sommerfeld enhancements in indirect detection

Abstract

Dark matter (DM) self-interactions have important implications for the formation and evolution of structure, from dwarf galaxies to clusters of galaxies. We study the dynamics of self-interacting DM via a light mediator, focusing on the quantum resonant regime where the scattering cross section has a non-trivial velocity dependence. While there are long-standing indications that observations of small scale structure in the Universe are not in accord with the predictions of collisionless DM, theoretical study and simulations of DM self-interactions have focused on parameter regimes with simple analytic solutions for the scattering cross section, with constant or classical velocity (and no angular) dependence. We devise a method that allows us to explore the velocity and angular dependence of self-scattering more broadly, in the strongly-coupled resonant and classical regimes where many partial modes are necessary for the achieving the result. We map out the entire parameter space of DM self-interactions --- and implications for structure observations --- as a function of the coupling and the DM and mediator masses. We derive a new analytic formula for describing resonant s-wave scattering. Finally, we show that DM self-interactions can be correlated with observations of Sommerfeld enhancements in DM annihilation through indirect detection experiments.