Dilution of Dark Matter Relic abundance due to First Order Electroweak Phase Transition

TL;DR

This paper explores how a first-order electroweak phase transition can dilute dark matter relic abundance in a specific particle physics model, affecting dark matter detection prospects and gravitational wave signals.

Contribution

It demonstrates the impact of a first-order electroweak phase transition on dark matter relic density within a complex singlet scalar extended $Z_3$-invariant type-II seesaw model, linking phase transition dynamics to dark matter constraints.

Findings

Dilution of dark matter relic density due to phase transition effects.

Parameter regions previously excluded become viable after considering dilution.

Connection established between phase transition-induced dilution and gravitational wave production.

Abstract

We investigate the effect of a first-order electroweak phase transition (FOEWPT), which is one of the prerequisites for electroweak baryogenesis, on the thermal relic abundance of the dark matter (DM) that freezes out before the occurrence of the phase transition in the complex singlet scalar extended $Z_3$-invariant type-II seesaw model that can simultaneously provide a DM candidate, explain the non-vanishing neutrino masses and the baryon asymmetry of the Universe. Such a phase transition around the electroweak scale leaves an impact on the relic density due to the release of entropy, particularly for a TeV-scale DM. We thus concentrate on the region of parameter space of the said model, which favors an FOEWPT in the early Universe and for which the DM is heavy such that its freeze-out temperature turns out to be larger than the phase transition temperature. We further study the dependencies of the dilution factor of the DM relic density on the model parameters, the nucleation temperature, the strength and the duration of the phase transition. Such a dilution might retrieve some of the regions of parameter space that were previously ruled out by the measured value of the DM relic density and/or the latest constraints from the DM direct-detection experiments. Furthermore, a direct connection is drawn between the dilution factor and the generation of stochastic gravitational waves as a result of an FOEWPT.