From Hubble to Bubble

TL;DR

This paper explores a new mechanism where a non-minimally coupled scalar field triggers a strong first-order phase transition after inflation, producing gravitational waves that could be detected in future experiments.

Contribution

It introduces a novel triggering mechanism for BSM phase transitions involving a dynamical double-well potential and curvature evolution, with potential GW signatures.

Findings

Phase transition can be triggered by potential barrier reduction due to curvature evolution.

Bubble nucleation and collision produce gravitational waves detectable by future observatories.

The mechanism works across different inflation scales and kination periods.

Abstract

The detection of a stochastic Gravitational Wave (GW) background sourced by a cosmological phase transition would allow us to see the early Universe from a completely new perspective, illuminating aspects of Beyond the Standard Model (BSM) physics and inflationary cosmology. In this study, we investigate whether the evolution of the scalar potential of a minimal SM extension after inflation can lead to a strong first-order phase transition. In particular, we focus on a BSM spectator scalar field that is non-minimally coupled to gravity and has a dynamical double-well potential. As inflation ends, the potential barrier diminishes due to the evolution of the curvature scalar. Therefore, a phase transition can proceed through the nucleation of true-vacuum bubbles that collide as they fill the Universe and produce GWs. We consider high and low scales of inflation, while also taking into account a kination period between inflation and the onset of radiation domination. With this prescription, we showcase a proof-of-concept study of a new triggering mechanism for BSM phase transitions in the early Universe, whose GW signatures could potentially be probed with future detectors.