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.
Highlights
The NANOGrav Collaboration has recently released their results for gravitational-wave (GW) background produced from a first-order phase transition (FOPT) in 45 pulsars from their 12.5 year data [1]
Motivated by the NANOGrav Collaboration’s recent analysis of their 12.5 yr data implying a possible origin of a stochastic GW spectrum from a first-order phase transition below the EW scale, we revisited the simplest possibility of a dark Abelian gauge extension of the standard model (SM)
While the SM fields are neutral under this gauge symmetry, a complex scalar singlet with nonvanishing gauge charge can lead to the necessary symmetry breaking
Summary
The NANOGrav Collaboration has recently released their results for gravitational-wave (GW) background produced from a first-order phase transition (FOPT) in 45 pulsars from their 12.5 year data [1]. [12,13,14,15,16,17,18] and references therein While such a strongly first-order dark phase transition and resulting gravitational waves have been discussed earlier as well, we study this possibility for the first time after the NANOGrav Collaboration analyzed their 12.5 year data in the context of gravitational waves from the FOPT at a low temperature below the EW scale [1]. We examine how tiny neutrino masses can be generated through a low-scale seesaw mechanism like a radiative or inverse seesaw, and a singlet fermion charged under Uð1ÞD can be a good dark matter candidate while keeping the model parameters consistent with the results from NANOGrav
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