Gravitational wave spectra from strongly supercooled phase transitions

TL;DR

This paper investigates gravitational wave spectra generated by strongly supercooled phase transitions, focusing on models with a complex scalar field and comparing results to real scalar field cases.

Contribution

It provides detailed lattice simulations of two-bubble collisions and computes GW spectra, highlighting differences due to U(1) symmetry.

Findings

Low-frequency spectrum scales as ω in U(1) symmetric case

Low-frequency spectrum scales as ω^3 for real scalar field

High-frequency spectrum decays as ω^{-2} in both cases

Abstract

We study gravitational wave (GW) production in strongly supercooled cosmological phase transitions, taking particular care of models featuring a complex scalar field with a U$(1)$ symmetric potential. We perform lattice simulations of two-bubble collisions to properly model the scalar field gradients, and compute the GW spectrum sourced by them using the thin-wall approximation in many-bubble simulations. We find that in the U$(1)$ symmetric case the low-frequency spectrum is $\propto\omega$ whereas for a real scalar field it is $\propto\omega^3$. In both cases the spectrum decays as $\omega^{-2}$ at high frequencies.