Lower bound on the electroweak wall velocity from hydrodynamic instability

TL;DR

This paper calculates the critical velocity below which subsonic bubble walls become hydrodynamically unstable during a first-order electroweak phase transition, impacting scenarios for electroweak baryogenesis.

Contribution

It provides the first detailed calculation of the hydrodynamic instability threshold for various Standard Model extensions.

Findings

Identifies parameter regions with stable deflagrations.

Shows conditions favorable for electroweak baryogenesis.

Provides critical velocity estimates for different models.

Abstract

The subsonic expansion of bubbles in a strongly first-order electroweak phase transition is a convenient scenario for electroweak baryogenesis. For most extensions of the Standard Model, stationary subsonic solutions (i.e., deflagrations) exist for the propagation of phase transition fronts. However, deflagrations are known to be hydrodynamically unstable for wall velocities below a certain critical value. We calculate this critical velocity for several extensions of the Standard Model and compare with an estimation of the wall velocity. In general, we find a region in parameter space which gives stable deflagrations as well as favorable conditions for electroweak baryogenesis.