Fluctuation-Induced Friction in Bubble-Wall Dynamics of Cosmological First-Order Phase Transitions
Abstract
We study bubble-wall dynamics in cosmological first-order phase transitions in a two-scalar-field model, where the wall is formed by φ 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 Tn, 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.