Velocity of electroweak bubble walls

TL;DR

This paper investigates the velocities of bubble walls during the electroweak phase transition across various models, highlighting implications for gravitational wave signals and baryogenesis based on wall velocity ranges.

Contribution

It provides estimates of bubble wall velocities in extended Standard Model scenarios, considering hydrodynamics and friction effects, and discusses their relevance for cosmological signals.

Findings

Deflagrations are generally more likely than detonations.

Models with extra bosons tend to have high wall velocities ($0.1 ext{ to }0.6$).

Models with extra fermions can have low wall velocities ($10^{-2} ext{ to }10^{-1}$).

Abstract

We study the velocity of bubble walls in the electroweak phase transition. For several extensions of the Standard Model, we estimate the friction and calculate the wall velocity, taking into account the hydrodynamics. We find that deflagrations are generally more likely than detonations. Nevertheless, for models with extra bosons, which give a strongly first-order phase transition, the deflagration velocity is in general quite high, $0.1\lesssim v_w\lesssim 0.6$. Therefore, such phase transitions may produce an important signal of gravitational waves. On the other hand, models with extra fermions which are strongly coupled to the Higgs boson may provide a strongly first-order phase transition and small velocities, $10^{-2}\lesssim v_w\lesssim 10^{-1}$, as required by electroweak baryogenesis.