Gravitational waves from defect-driven phase transitions: domain walls

TL;DR

This paper investigates how domain wall networks influence gravitational wave signals from first-order phase transitions, revealing shifts to lower frequencies and increased amplitudes, relevant for recent PTA gravitational wave observations.

Contribution

It introduces a detailed analysis of gravitational waves from domain wall-seeded phase transitions, highlighting their distinctive spectral features compared to homogeneous transitions.

Findings

Gravitational wave signals are shifted to lower frequencies with higher amplitudes due to domain walls.

The setup explains features consistent with recent PTA gravitational wave hints.

Larger domain wall correlation lengths significantly impact the gravitational wave spectrum.

Abstract

We discuss the gravitational wave spectrum produced by first-order phase transitions seeded by domain wall networks. This setup is important for many two-step phase transitions as seen for example in the singlet extension of the standard model. Whenever the correlation length of the domain wall network is larger than the typical bubble size, this setup leads to a gravitational wave signal that is shifted to lower frequencies and with an enhanced amplitude compared to homogeneous phase transitions without domain walls. We discuss our results in light of the recent PTA hints for gravitational waves.