Electroweak bubble wall expansion: gravitational waves and baryogenesis in Standard Model-like thermal plasma

TL;DR

This paper calculates the properties of electroweak bubble walls in various models to predict baryogenesis and gravitational wave signals, finding that observable signals are likely only from strong, relativistic transitions.

Contribution

It introduces a semi-classical method to determine bubble wall velocity and thickness in SM-like models, linking these to baryogenesis and gravitational wave predictions.

Findings

Singlet extension can produce observed baryon asymmetry but no detectable gravitational waves.

Effective field theory constraints prevent explaining baryon abundance, yet some signals may be within LISA's sensitivity.

Weak transitions produce signals too faint for future gravitational wave detection.

Abstract

Computing the properties of the bubble wall of a cosmological first order phase transition at electroweak scale is of paramount importance for the correct prediction of the baryon asymmetry of the universe and the spectrum of gravitational waves. By means of the semi-classical formalism we calculate the velocity and thickness of the wall using as theoretical framework the scalar singlet extension of the SM with a parity symmetry and the SM effective field theory supplemented by a dimension six operator. We use these solutions to carefully predict the baryon asymmetry and the gravitational wave signals. The singlet scenario can easily accommodate the observed asymmetry but these solutions do not lead to observable effects at future gravity wave experiments. In contrast the effective field theory fails at explaining the baryon abundance due to the strict constraints from electric dipole moment experiments, however, the strongest solutions we found fall within the sensitivity of the LISA experiment. We provide a simple analytical approximation for the wall velocity which only requires calculation of the strength and temperature of the transition and works reasonably well in all models tested. We find that generically the weak transitions where the fluid approximation can be used to calculate the wall velocity and verify baryogenesis produce signals too weak to be observed in future gravitational wave experiments. Thus, we infer that GW signals produced by simple SM extensions visible in future experiments are likely to only be produced in strong transitions described by detonations with highly relativistic wall velocities.