Self-interacting dark matter from late decays and the $H_0$ tension

TL;DR

This paper proposes a mechanism where late decays produce self-interacting dark matter, which can alleviate the Hubble tension and small-scale structure issues in cosmology, demonstrated within the Higgs portal model.

Contribution

It introduces a novel late decay process for dark matter production that addresses multiple cosmological tensions simultaneously.

Findings

Late decays produce self-interacting dark matter after recombination.

The mechanism relaxes the Hubble tension.

The Higgs portal model effectively realizes this process.

Abstract

We investigate a mechanism for the production of self-interacting dark matter based on WIMP-like messenger state decays into dark matter and dark radiation occurring after recombination. Such a transition leads to a mild relaxation of the Hubble tension, and at the same time may resolve the small-scale structure problems of the $\Lambda$CDM. We illustrate this mechanism in the Higgs portal dark matter model, which we find to be a promising route.