Spinodal Gravitational Waves

TL;DR

This paper introduces a novel gravitational-wave generation mechanism during cosmological phase transitions, specifically when the universe supercools into the spinodal region, leading to a distinct spectrum from traditional bubble nucleation.

Contribution

It reveals the spinodal transition as an alternative to bubble nucleation in first-order phase transitions and models this process using holography in strongly coupled gauge theories.

Findings

Distinct gravitational wave spectrum from spinodal dynamics

Supercooling can lead to spinodal transition instead of bubble nucleation

Potential thermal inflation preceding spinodal transition

Abstract

We uncover a new gravitational-wave production mechanism in cosmological, first-order, thermal phase transitions. These are usually assumed to proceed via the nucleation of bubbles of the stable phase inside the metastable phase. However, if the nucleation rate is sufficiently suppressed, then the Universe may supercool all the way down the metastable branch and enter the spinodal region. In this case the transition proceeds via the exponential growth of unstable modes and the subsequent formation, merging and relaxation of phase domains. We use holography to follow the real-time evolution of this process in a strongly coupled, four-dimensional gauge theory. The resulting gravitational wave spectrum differs qualitatively from that in transitions mediated by bubble nucleation. We discuss the possibility that the spinodal dynamics may be preceded by a period of thermal inflation.