Gravitational waves from the sound shell model: direct and inverse phase transitions in the early Universe

TL;DR

This paper compares gravitational wave signals from direct and inverse cosmological phase transitions using the sound shell model, highlighting observable differences and potential for experimental discrimination.

Contribution

It introduces a detailed analysis of gravitational wave spectra from both transition types within the sound shell model framework, expanding understanding of early Universe phenomena.

Findings

Distinct gravitational wave signatures for direct and inverse transitions

Potential to differentiate transition types through gravitational wave observations

Enhanced understanding of fluid dynamics in cosmological phase transitions

Abstract

Cosmological phase transitions are a frequent phenomenon in particle physics models beyond the Standard Model, and the corresponding gravitational wave signal offers a key probe of new physics in the early Universe. Depending on the underlying microphysics, the transition can exhibit either direct or inverse hydrodynamics, leading to a different phenomenology. Most studies to date have focused on direct transitions, where the cosmic fluid is pushed or dragged by the expanding vacuum bubbles. In contrast, inverse phase transitions are characterized by fluid profiles where the plasma is sucked in by the expanding bubbles. Using the sound shell model, we derive and compare the gravitational wave spectra from sound waves for direct and inverse phase transitions, providing new insights into the potential observable features and the possibility of discriminating among the various fluid solutions in gravitational wave experiments.