Phases of Cannibal Dark Matter

TL;DR

This paper explores the different phases of hidden sector cannibalism and their impact on dark matter relic density, revealing novel behaviors and potential observable effects in cosmology.

Contribution

It identifies three new phases of hidden sector evolution during dark matter freeze-out, detailing their unique phenomenology and cosmological signatures.

Findings

Three distinct phases of hidden sector evolution are characterized.

Different phases lead to observable effects like boosted annihilation rates and CMB distortions.

The relic density of dark matter depends on the phase during freeze-out.

Abstract

A hidden sector with a mass gap undergoes an epoch of cannibalism if number changing interactions are active when the temperature drops below the mass of the lightest hidden particle. During cannibalism, the hidden sector temperature decreases only logarithmically with the scale factor. We consider the possibility that dark matter resides in a hidden sector that underwent cannibalism, and has relic density set by the freeze-out of two-to-two annihilations. We identify three novel phases, depending on the behavior of the hidden sector when dark matter freezes out. During the cannibal phase, dark matter annihilations decouple while the hidden sector is cannibalizing. During the chemical phase, only two-to-two interactions are active and the total number of hidden particles is conserved. During the one way phase, the dark matter annihilation products decay out of equilibrium, suppressing the production of dark matter from inverse annihilations. We map out the distinct phenomenology of each phase, which includes a boosted dark matter annihilation rate, new relativistic degrees of freedom, warm dark matter, and observable distortions to the spectrum of the cosmic microwave background.