Gravitational Waves from Feebly Interacting Particles in a First Order Phase Transition

TL;DR

This paper explores a new mechanism for gravitational wave production during first order phase transitions, where energy is transferred to feebly interacting particles, resulting in distinct observable signals.

Contribution

It introduces a formalism for GW generation from free-streaming feebly interacting particles, a novel scenario not previously considered in phase transition models.

Findings

Distinct GW signatures from feebly interacting particles

Potential observability with near-future detectors

New formalism for non-plasma GW sources

Abstract

First order phase transitions are well-motivated and extensively studied sources of gravitational waves (GWs) from the early Universe. The vacuum energy released during such transitions is assumed to be transferred primarily either to the expanding bubble walls, whose collisions source GWs, or to the surrounding plasma, producing sound waves and turbulence, which source GWs. In this Letter, we study an alternative possibility that has not yet been considered: the released energy gets transferred primarily to feebly interacting particles that do not form a coherent interacting plasma but simply free-stream individually. We develop the formalism to study the production of GWs from such configurations, and demonstrate that such GW signals have qualitatively distinct characteristics compared to conventional sources and are potentially observable with near-future GW detectors.