Single-step first order phase transition and gravitational waves in a SIMP dark matter scenario

TL;DR

This paper explores a sub-GeV scalar dark matter model with 3→2 annihilations, revealing a potential first order phase transition at low temperatures that could generate detectable gravitational waves.

Contribution

It demonstrates the possibility of a first order phase transition in a SIMP dark matter scenario and calculates the resulting gravitational wave signals.

Findings

First order phase transition can occur at sub-GeV temperatures.

Gravitational wave spectra from the transition are computed.

Model explains observed relic abundance with specific thermal potential shape.

Abstract

We investigate the non-zero temperature dynamics of a sub-GeV dark matter scenario freezing-out via self-interactions. As a prototype, we take up the case of a scalar dark matter species undergoing $3 \to 2$ number changing annihilations catalysed by another scalar. We study the shape of the thermal potential of this scenario in a parameter region accounting for the observed relic abundance. An analysis reveals the possibility of a first order phase transition with bubble nucleation occurring at sub-GeV temperatures. This finding can be correlated with the typical sub-GeV masses in the framework. The gravitational wave spectra associated with such a phase transition is subsequently computed.