Gravitational waves from breaking of an extra U(1) in SO(10) grand unification

Abstract

In a class of gauged $U(1)$ extended Standard Models (SMs), the breaking of the $U(1)$ symmetry is not only a source for Majorana masses of right-handed (RH) neutrinos crucial for the seesaw mechanism, but also a source of stochastic gravitational wave (GW) background. Such U(1) extended models are well-motivated from the viewpoint of grand unification. In this paper, we discuss a successful ultraviolet completion of a U(1) extended SM by an SO(10) grand unified model through an intermediate step of SU(5) × U(1) unification. With a parameter set that is compatible with the SO(10) grand unification, we find that a first-order phase transition associated with the U(1) symmetry breaking can be strong enough to generate GWs with a detectable size of amplitude. We also find that the resultant GW amplitude reduces and its peak frequency becomes higher as the RH neutrino masses increase.