Dark matter self-interactions in the matter power spectrum

TL;DR

This paper investigates how self-interacting light dark matter in secluded sectors influences the matter power spectrum, revealing that such interactions can relax existing constraints and produce observable differences from standard cold dark matter models.

Contribution

It provides a comprehensive analysis of self-interacting light dark matter effects on the matter power spectrum using Boltzmann solvers, including realistic interaction regimes and specific dark QCD-like models.

Findings

Self-interactions relax the Lyman-alpha bound on dark matter mass.

Qualitative differences from $\\Lambda$CDM appear for light, self-interacting dark matter.

Matter power spectrum varies significantly across different interaction regimes.

Abstract

We study the imprints of secluded dark sectors with a mass gap and self-interactions on the matter power spectrum. When Dark Matter (DM) is sufficiently light, in the ballpark of a few KeV, and self-interacting we find qualitative difference with respect to $\Lambda$CDM and also to free streaming DM. In order to emphasize the role of interactions for the evolution of the primordial perturbations we discuss various regimes: ranging from the ideal case of a tightly coupled perfect fluid to the free case of Warm Dark Matter, including the realistic case of small but non-vanishing self-interactions. We compute the matter power spectrum in all these regimes with the aid of Boltzmann solvers. Light dark sectors with self-interactions are efficiently constrained by Lyman-$\alpha$ data and we find that the presence of self-interactions relaxes the bound on the DM mass. As a concrete realization we study models with dark QCD-like sectors, where DM is made of light dark-pions.