Hydrodynamics of phase transition fronts and the speed of sound in the plasma

TL;DR

This paper investigates the hydrodynamics of phase transition fronts in cosmology, revealing that realistic models with lower sound speeds lead to new solutions and affect latent heat transfer efficiency.

Contribution

It introduces the impact of lower sound speeds in realistic models on hydrodynamics and uncovers new solution types absent in the bag model approximation.

Findings

Lower sound speeds in the low-temperature phase alter hydrodynamic solutions.

A new hydrodynamical solution type is identified.

Analytic expressions for latent heat transfer efficiency are derived.

Abstract

The growth of bubbles in cosmological first-order phase transitions involves nontrivial hydrodynamics. For that reason, the study of the propagation of phase transition fronts often requires several approximations. A frequently used approximation consists in describing the two phases as being composed only of radiation and vacuum energy (the so-called bag equation of state). We show that, in realistic models, the speed of sound in the low-temperature phase is generally smaller than that of radiation, and we study the hydrodynamics in such a situation. We find in particular that a new kind of hydrodynamical solution may be possible, which does not arise in the bag model. We obtain analytic results for the efficiency of the transfer of latent heat to bulk motions of the plasma, as a function of the speed of sound in each phase.