Cannibalism's lingering imprint on the matter power spectrum

TL;DR

This paper explores how dark sector thermalization and cannibal self-interactions in the early universe can influence the matter power spectrum, especially on small scales, potentially affecting dark matter structure formation.

Contribution

It introduces a framework linking dark sector particle properties with modifications to the matter power spectrum caused by cannibal behavior in the early universe.

Findings

Cannibal self-interactions can set the small-scale cutoff in the matter power spectrum.

An epoch of early matter domination driven by a cannibal species impacts dark matter structures.

The model provides a mapping between particle properties and cosmological perturbation features.

Abstract

The early universe may have contained internally thermalized dark sectors that were decoupled from the Standard Model. In such scenarios, the relic dark thermal bath, composed of the lightest particle in the dark sector, can give rise to an epoch of early matter domination prior to Big Bang Nucleosynthesis, which has a potentially observable impact on the smallest dark matter structures. This lightest dark particle can easily and generically have number-changing self-interactions that give rise to "cannibal" behavior. We consider cosmologies where an initially sub-dominant cannibal species comes to temporarily drive the expansion of the universe, and we provide a simple map between the particle properties of the cannibal species and the key features of the enhanced dark matter perturbation growth in such cosmologies. We further demonstrate that cannibal self-interactions can determine the small-scale cutoff in the matter power spectrum even when the cannibal self-interactions freeze out prior to cannibal domination.