Implications of Two-component Dark Matter Induced by Forbidden Channels and Thermal Freeze-out

TL;DR

This paper proposes a two-component dark matter model where relic densities are set by forbidden channels and thermal freeze-out, leading to potential solutions for small scale structure problems and testable predictions for experiments like SHiP.

Contribution

It introduces a novel two-component dark matter framework with forbidden channels and spontaneous symmetry breaking, highlighting unique relic density mechanisms and experimental implications.

Findings

Forbidden channels can dominate relic density of lighter dark matter

Large self-interactions can address small scale structure issues

Parameter space testable by SHiP experiment

Abstract

We consider a model of two-component dark matter based on a hidden $U(1)_D$ symmetry, in which relic densities of the dark matter are determined by forbidden channels and thermal freeze-out. The hidden $U(1)_D$ symmetry is spontaneously broken to a residual $\mathbb{Z}_4$ symmetry, and the lightest $\mathbb{Z}_4$ charged particle can be a dark matter candidate. Moreover, depending on the mass hierarchy in the dark sector, we have two-component dark matter. We show that the relic density of the lighter dark matter component can be determined by forbidden annihilation channels which require larger couplings compared to the normal freeze-out mechanism. As a result, a large self-interaction of the lighter dark matter component can be induced, which may solve small scale problems of $\Lambda$CDM model. On the other hand, the heavier dark matter component is produced by normal freeze-out mechanism. We find that interesting implications emerge between the two dark matter components in this framework. We explore detectabilities of these dark matter particles and show some parameter space can be tested by the SHiP experiment.