Bubble wall velocities with an extended fluid Ansatz

TL;DR

This paper models the bubble wall velocity during cosmological phase transitions using an extended fluid Ansatz, revealing the importance of higher order effects and their impact on the nature of solutions.

Contribution

It introduces an extended fluid Ansatz to better model plasma effects and explores how particle content influences bubble wall solutions.

Findings

Higher order terms significantly affect bubble wall velocities.

In Standard Model-like scenarios, only deflagrations are viable.

Different particle content can alter the solution type.

Abstract

We compute the terminal bubble wall velocity during a cosmological phase transition by modelling non-equilibrium effects in the plasma with the so-called "extended fluid Ansatz". A $\phi^6$ operator is included in the Standard Model effective potential to mimic effects of new physics. Hydrodynamical heating of the plasma ahead of the bubble is taken into account. We find that the inclusion of higher order terms in the fluid Ansatz is typically relevant, and may even turn detonation solutions into deflagrations. Our results also corroborate recent findings in the literature that, for a Standard Model particle content in the plasma, only deflagration solutions are viable. However, we also show that this outcome may be altered in a theory with a different particle content.