Gravitational waves from a dark $U(1)_D$ phase transition in the light of NANOGrav 12.5 yr data

TL;DR

This paper explores how a first-order phase transition in a $U(1)_D$ gauge extension of the standard model can produce gravitational waves consistent with NANOGrav 12.5-year data, and discusses implications for dark matter and neutrino masses.

Contribution

It identifies the parameter space of a minimal $U(1)_D$ model that explains NANOGrav gravitational wave signals and links it to dark matter and neutrino mass generation mechanisms.

Findings

Parameter space consistent with NANOGrav data identified

Dark matter can arise from a singlet fermion charged under $U(1)_D$

Additional fields can generate light neutrino masses

Abstract

We study a possibility of a strong first-order phase transition (FOPT) taking place below the electroweak scale in the context of $U(1)_D$ gauge extension of the standard model. As pointed out recently by the NANOGrav collaboration, gravitational waves from such a phase transition with appropriate strength and nucleation temperature can explain their 12.5 yr data. We first find the parameter space of this minimal model consistent with NANOGrav findings considering only a complex singlet scalar and $U(1)_D$ vector boson. Existence of a singlet fermion charged under $U(1)_D$ can give rise to dark matter in this model, preferably of non-thermal type, while incorporating additional fields can also generate light neutrino masses through typical low scale seesaw mechanisms like radiative or inverse seesaw.