Friction pressure on relativistic bubble walls

TL;DR

This paper develops a non-perturbative method to compute the pressure exerted on relativistic bubble walls during a cosmological phase transition, accounting for gauge boson radiation and various physical effects.

Contribution

It introduces a resummation technique for gauge boson emissions at all leading-log orders, providing a quantitative analysis of the resulting pressure on bubble walls.

Findings

Radiated bosons are predominantly soft.

Retarding pressure is linear in Lorentz boost and order parameter.

The method accounts for IR cut-offs, wall thickness, and reflection effects.

Abstract

During a cosmological first-order phase transition, particles of the plasma crossing the bubble walls can radiate a gauge boson. The resulting pressure cannot be computed perturbatively for large coupling constant and/or large supercooling. We resum the real and virtual emissions at all leading-log orders, both analytically and numerically using a Monte-Carlo simulation. We find that radiated bosons are dominantly soft and that the resulting retarding pressure on relativistic bubble walls is linear both in the Lorentz boost and in the order parameter, up to a log. We further quantitatively discuss IR cut-offs, wall thickness effects, the impact of various approximations entering the calculation, and comment on the fate of radiated bosons that are reflected.