Energy Budget of Cosmological First-order Phase Transitions

TL;DR

This paper analyzes the hydrodynamics of bubble growth in first-order cosmological phase transitions across various regimes, highlighting implications for baryogenesis and gravitational wave predictions without relying on specific particle physics models.

Contribution

It provides a comprehensive study of bubble expansion regimes and calculates energy transfer efficiencies, clarifying conditions for runaway solutions in strong first-order transitions.

Findings

Runaway solutions lead to most energy in the bubble wall.

Fluid motions are minimal in strong transitions with runaway bubbles.

Implications for gravitational wave signals are significant in most models.

Abstract

The study of the hydrodynamics of bubble growth in first-order phase transitions is very relevant for electroweak baryogenesis, as the baryon asymmetry depends sensitively on the bubble wall velocity, and also for predicting the size of the gravity wave signal resulting from bubble collisions, which depends on both the bubble wall velocity and the plasma fluid velocity. We perform such study in different bubble expansion regimes, namely deflagrations, detonations, hybrids (steady states) and runaway solutions (accelerating wall), without relying on a specific particle physics model. We compute the efficiency of the transfer of vacuum energy to the bubble wall and the plasma in all regimes. We clarify the condition determining the runaway regime and stress that in most models of strong first-order phase transitions this will modify expectations for the gravity wave signal. Indeed, in this case, most of the kinetic energy is concentrated in the wall and almost no turbulent fluid motions are expected since the surrounding fluid is kept mostly at rest.