Cosmological constraints on multi-interacting dark matter

TL;DR

This paper explores the effects of dark matter interacting with photons, baryons, and dark radiation on cosmological observations, introducing a new code to analyze such scenarios and showing potential to reduce existing cosmological tensions.

Contribution

It develops a novel Boltzmann code allowing for multiple simultaneous dark matter interactions and reassesses cosmological bounds in these complex models.

Findings

No significant degeneracies between different interactions.

Interactions are largely additive in their effects.

Combination of interactions can reduce cosmological tensions in $S_8$ and $H_0$.

Abstract

The increasingly significant tensions within $\Lambda$CDM, combined with the lack of detection of dark matter (DM) in laboratory experiments, have boosted interest in non-minimal dark sectors, which are theoretically well-motivated and inspire new search strategies for DM. Here we consider, for the first time, the possibility of DM having simultaneous interactions with photons, baryons, and dark radiation (DR). We have developed a new and efficient version of the Boltzmann code CLASS that allows for one DM species to have multiple interaction channels. With this framework we reassess existing cosmological bounds on the various interaction coefficients in multi-interacting DM scenarios. We find no clear degeneracies between these different interactions and show that their cosmological effects are largely additive. We further investigate the possibility of these models to alleviate the cosmological tensions, and find that the combination of DM-photon and DM-DR interactions can at the same time reduce the $S_8$ tension (from $2.3\sigma$ to $1.2\sigma$) and the $H_0$ tension (from $4.3\sigma$ to $3.1\sigma$). The public release of our code will pave the way for the study of various rich dark sectors.