Gravitational waves from first order electroweak phase transition in models with the $U(1)_X^{}$ gauge symmetry

TL;DR

This paper explores gravitational waves from first order phase transitions in a model extending the Standard Model with a dark $U(1)_X$ gauge symmetry, analyzing their detectability and collider constraints.

Contribution

It demonstrates that multi-step phase transitions in this model can produce detectable gravitational waves at future space-based interferometers, considering collider and dark sector constraints.

Findings

Detectable GWs are possible if the dark photon is heavier than 25 GeV.

Collider bounds exclude some parameter space for GW detection.

Future GW detectors like LISA and DECIGO can observe signals from these phase transitions.

Abstract

We consider a standard model extension equipped with a dark sector where the $U(1)_X^{}$ Abelian gauge symmetry is spontaneously broken by the dark Higgs mechanism. In this framework, we investigate patterns of the electroweak phase transition as well as those of the dark phase transition, and examine detectability of gravitational waves (GWs) generated by such strongly first order phase transition. It is pointed out that the collider bounds on the properties of the discovered Higgs boson exclude a part of parameter space that could otherwise generate detectable GWs. After imposing various constraints on this model, it is shown that GWs produced by multi-step phase transitions are detectable at future space-based interferometers, such as LISA and DECIGO, if the dark photon is heavier than 25 GeV. Furthermore, we discuss the complementarity of dark photon searches or dark matter searches with the GW observations in these models with the dark gauge symmetry.