Bubble Clustering in Cosmological First Order Phase Transitions

TL;DR

This paper investigates the spatial correlations of bubble nucleation sites during false vacuum decay in cosmological phase transitions, revealing clustering patterns that could impact gravitational wave signals and bubble collision probabilities.

Contribution

It introduces a semi-classical stochastic method to analyze bubble nucleation correlations, showing that nucleation sites tend to cluster similarly to Gaussian field peaks, which is a novel insight.

Findings

Bubble nucleation sites exhibit clustering behavior.

Clustering resembles peaks in Gaussian fields.

Implications for gravitational wave spectra and bubble collision probabilities.

Abstract

False vacuum decay in quantum mechanical first order phase transitions is a phenomenon with wide implications in cosmology, and presents interesting theoretical challenges. In the standard approach, it is assumed that false vacuum decay proceeds through the formation of bubbles that nucleate at random positions in spacetime and subsequently expand. In this paper we investigate the presence of correlations between bubble nucleation sites using a recently proposed semi-classical stochastic description of vacuum decay. This procedure samples vacuum fluctuations, which are then evolved using classical lattice simulations. We compute the two-point function for bubble nucleation sites from an ensemble of simulations, demonstrating that nucleation sites cluster in a way that is qualitatively similar to peaks in random Gaussian fields. We qualitatively assess the phenomenological implications of bubble clustering in early Universe phase transitions, which include features in the power spectrum of stochastic gravitational waves and an enhancement or suppression of the probability of observing bubble collisions in the eternal inflation scenario.