Bubble nucleation and growth in very strong cosmological phase transitions

TL;DR

This paper investigates the dynamics of very strong cosmological phase transitions, focusing on bubble nucleation rates, their approximations, and implications for cosmic phenomena like gravitational waves.

Contribution

It introduces a Gaussian approximation for nucleation rates in strong phase transitions and analytically solves their evolution, expanding beyond the traditional exponential model.

Findings

Gaussian approximation can be more suitable near the transition limit

Analytical solutions for phase transition evolution are derived

Implications for gravitational wave signals are discussed

Abstract

Strongly first-order phase transitions, i.e., those with a large order parameter, are characterized by a considerable supercooling and high velocities of phase transition fronts. A very strong phase transition may have important cosmological consequences due to the departures from equilibrium caused in the plasma. In general, there is a limit to the strength, since the metastability of the old phase may prevent the transition to complete. Near this limit, the bubble nucleation rate achieves a maximum and thus departs from the widely assumed behavior in which it grows exponentially with time. We study the dynamics of this kind of phase transitions. We show that in some cases a gaussian approximation for the nucleation rate is more suitable, and in such a case we solve analytically the evolution of the phase transition. We compare the gaussian and exponential approximations with realistic cases and we determine their ranges of validity. We also discuss the implications for cosmic remnants such as gravitational waves.