Phase transitions in the singlet majoron model

Abstract

We consider the space of parameters and study the nature of phase transitions in the singlet majoron model. We show that the phase transition typically proceeds in two steps: the global U(1) breaks first in a very weakly first order transition, followed by electroweak breaking. The latter may give rise to considerable release of latent heat. We impose the LEP limit of the scalar particle production rate on the model, and if baryogenesis is assumed to take place at the electroweak phase transition, baryon number dilution by sphalerons constrains the parameters further. A small portion of the parameter space may, however, survive both the constraints.