Cannibal domination and the matter power spectrum

TL;DR

This paper explores how a cannibal-dominated era in the early universe affects small-scale structure formation, revealing a characteristic peak in the matter power spectrum linked to hidden sector properties.

Contribution

It is the first to analyze the impact of a cannibal-dominated epoch on the matter power spectrum and structure formation, connecting hidden sector dynamics to observable cosmological features.

Findings

A characteristic peak in the dark matter power spectrum due to cannibal era

Early microhalo formation influenced by cannibal particle properties

Imprints on small-scale structure without direct dark matter Standard Model couplings

Abstract

Decoupled hidden sectors can easily and generically result in a period of cannibal domination, during which the dominant component of the Universe has an equation of state intermediate between radiation and matter due to self-heating by number-changing interactions. We present for the first time the consequences of a cannibal-dominated era prior to big bang nucleosynthesis for structure formation on small scales. We find that an early cannibal-dominated era imprints a characteristic peak on the dark matter power spectrum, with scale and amplitude directly determined by the mass, lifetime, and number-changing interaction strength of the cannibal field. This enhancement to the small-scale matter power spectrum will generate early-forming dark matter microhalos, and we provide a detailed and transparent map between the properties of the cannibal species and the characteristic mass and formation time of these structures. These relations demonstrate how the internal workings of a hidden sector leave a potentially observable imprint on the matter power spectrum even if dark matter has no direct couplings to the Standard Model.