Filtered pseudo-scalar dark matter and gravitational waves from first order phase transition

TL;DR

This paper investigates how a first order phase transition in the hidden sector affects pseudo-scalar dark matter's relic abundance through a filtering-out effect and explores associated gravitational wave signals as potential observational evidence.

Contribution

It introduces a detailed analysis of the filtering-out effect for pseudo-scalar dark matter during a first order phase transition and connects it with gravitational wave predictions.

Findings

Filtering-out effect reduces dark matter relic abundance.

Gravitational wave signals can serve as signatures of the phase transition.

Dependence of filtering efficiency on bubble wall velocity and dark matter thermal status.

Abstract

If dark matter (DM) acquires mass during a first order phase transition, there will be a filtering-out effect when DM enters the expanding bubble. In this paper we study the filtering-out effect for a pseudo-scalar DM, whose mass may partially come from a first order phase transition in the hidden sector. We calculate the ratio of DM that may enter the bubble for various bubble wall velocities as well as various status of DM (in the thermal equilibrium, or out of the thermal equilibrium) at the time of phase transition, which results in small penetration rate that may affect the final relic abundance of the DM. We further study the stochastic gravitational wave signals emitted by the hidden sector phase transition at the space-based interferometer experiments as the smoking-gun of this model.