Self-Interacting Dark Matter in Cosmology: accurate numerical implementation and observational constraints

TL;DR

This paper develops a precise numerical method to model self-interacting dark matter perturbations in cosmology, enabling detailed analysis of their effects on structure formation and observational constraints.

Contribution

It introduces an accurate numerical implementation of Boltzmann hierarchies for self-interacting dark matter, surpassing traditional fluid approximations, and applies it to realistic DM candidates with observational implications.

Findings

New lower bounds on dark matter particle mass from structure formation data.

Demonstrated the impact of self-interactions on linear cosmological perturbations.

Provided a publicly available Boltzmann code for future research.

Abstract

This paper presents a systematic and accurate treatment of the evolution of cosmological perturbations in self-interacting dark matter models, for particles which decoupled from the primordial plasma while relativistic. We provide a numerical implementation of the Boltzmann hierarchies developed in a previous paper [JCAP, 09 (2020) 041] in a publicly available Boltzmann code and show how it can be applied to realistic DM candidates such as sterile neutrinos either under resonant or non-resonant production mechanisms, and for different field mediators. At difference with traditional fluid approximations -- also known as a $c_{\rm eff}-c_{\rm vis}$ parametrizations -- our approach follows the evolution of phase-space perturbations under elastic DM interactions for a wide range of interaction models, including the effects of late kinetic decoupling. Finally, we analyze the imprints left by different self interacting models on linear structure formation, which can be constrained using Lyman-$\alpha$ forest and satellite counts. We find new lower bounds on the particle mass that are less restrictive than previous constraints.