Energy budget of cosmological first-order phase transition in FLRW background

TL;DR

This paper investigates the hydrodynamics of bubble expansion during cosmological first-order phase transitions in an expanding universe, revealing that slower transitions reduce energy transfer efficiency and impact gravitational wave signals.

Contribution

It provides new insights into how the expansion of the universe affects energy transfer during phase transitions, especially for slow transitions, which was not thoroughly studied before.

Findings

Efficiency of energy transfer into bulk fluid motion is significantly reduced for slow transitions.

Sound wave contribution to gravitational waves is less dominant than previously thought.

Expansion of the universe influences hydrodynamics of phase transition bubbles.

Abstract

We study the hydrodynamics of bubble expansion in cosmological first-order phase transition in the Friedmann-Lema\^{\i}tre-Robertson-Walker (FLRW) background with probe limit. Different from previous studies for fast first-order phase transition in flat background, we find that, for slow first-order phase transition in FLRW background with a given peculiar velocity of the bubble wall, the efficiency factor of energy transfer into bulk motion of thermal fluid is significantly reduced, thus decreasing the previously-thought dominated contribution from sound wave to the stochastic gravitational-wave background.