The Cosmological Evolution of Self-interacting Dark Matter

TL;DR

This paper investigates how self-interacting dark matter influences cosmological structures, revealing unique signatures like dark acoustic oscillations and providing updated constraints on dark matter models using a new computational approach.

Contribution

It introduces a new Boltzmann code to analyze the linear power spectrum of self-interacting dark matter and compares its effects to warm dark matter, deriving new observational bounds.

Findings

Self-interactions cause dark acoustic oscillations in the matter power spectrum.

Current data disfavors warm dark matter below 5.3 keV, but self-interactions relax this limit to 4.4 keV.

The analysis sets new bounds on light scalar singlet dark matter.

Abstract

We study the evolution of cosmological perturbations in dark-matter models with elastic and velocity-independent self interactions. Such interactions are imprinted in the matter-power spectrum as dark acoustic oscillations, which can be experimentally explored to determine the strength of the self scatterings. Models with self interactions have similarities to warm dark matter, as they lead to suppression of power on small scales when the dark-matter velocity dispersion is sizable. Nonetheless, both the physical origin and the extent of the suppression differ for self-interacting dark matter from conventional warm dark matter, with a dark sound horizon controlling the reduction of power in the former case, and a free-streaming length in the latter. We thoroughly analyze these differences by performing computations of the linear power spectrum using a newly developed Boltzmann code. We find that while current Lyman-$\alpha$ data disfavor conventional warm dark matter with a mass less than 5.3 keV, when self interactions are included at their maximal value consistent with bounds from the Bullet Cluster, the limits are relaxed to 4.4 keV. Finally, we make use of our analysis to set novel bounds on light scalar singlet dark matter.