Fluctuation-Induced Friction in Bubble-Wall Dynamics of Cosmological First-Order Phase Transitions

TL;DR

This paper investigates how fluctuations in an additional scalar field influence bubble-wall dynamics during cosmological phase transitions, revealing a fluctuation-induced friction effect that alters wall propagation and has implications for gravitational waves and baryogenesis.

Contribution

It introduces a novel study of fluctuation-induced friction in bubble-wall dynamics using lattice simulations in a two-scalar-field model, highlighting the impact of scalar fluctuations on wall velocity and propagation profiles.

Findings

Fluctuations cause the wall to alternate between acceleration and deceleration.

The wall approaches a quasi-stationary regime with reduced average speed.

Propagation profiles include deflagration, detonation, and hybrid types.

Abstract

We study bubble-wall dynamics in cosmological first-order phase transitions in a two-scalar-field model, where the wall is formed by $\phi$ and an additional real scalar $s$ couples through a portal interaction. We evolve the coupled classical field equations on the lattice and demonstrate that for an initial Bose--Einstein distribution of $s$ fluctuations at the nucleation temperature $T_n$, the resulting patchy background intermittently modulates the local driving pressure on the wall. The wall therefore undergoes alternating episodes of acceleration and deceleration and approaches a quasi-stationary propagation regime with a smaller time-averaged speed than in the decoupled limit. We further identify three familiar propagation profiles -- deflagration, detonation, and hybrid -- distinguished by where the dynamical $s$-sector energy density is concentrated relative to the wall. These effects can impact gravitational wave and baryogenesis predictions.