General backreaction force of cosmological bubble expansion

TL;DR

This paper generalizes the understanding of backreaction forces in cosmological bubble expansion, which are crucial for predicting gravitational wave spectra from early universe phase transitions.

Contribution

It extends previous models by including backreaction forces beyond the simple bag equation of state, offering a more comprehensive analysis of bubble dynamics.

Findings

Generalized backreaction force beyond the bag model

Enhanced understanding of bubble wall, sound shell, and shock-wave interactions

Implications for gravitational wave predictions from phase transitions

Abstract

The gravitational-wave energy-density spectra from cosmological first-order phase transitions crucially depend on the terminal wall velocity of asymptotic bubble expansion when the driving force from the effective potential difference is gradually balanced by the backreaction force from the thermal plasma. Much attention has previously focused on the backreaction force acting on the bubble wall alone but overlooked the backreaction forces on the sound shell and shock-wave front, if any, which have been both numerically and analytically accomplished in our previous studies but only for a bag equation of state. In this paper, we will generalize the backreaction force on bubble expansion beyond the simple bag model.