Study of gravitational radiation from cosmic domain walls

TL;DR

This study investigates the gravitational wave background produced by cosmic domain walls, using numerical simulations and semi-analytical methods to analyze the spectrum's shape and characteristic frequencies.

Contribution

It introduces a dual-method approach to evaluate the gravitational wave spectrum from domain walls, including a semi-analytical technique for unresolved frequencies.

Findings

Spectrum slope changes at characteristic frequencies

Spectrum is flat or slightly red tilted between these frequencies

Semi-analytical method complements numerical simulations

Abstract

In this paper, following the previous study, we evaluate the spectrum of gravitational wave background generated by domain walls which are produced if some discrete symmetry is spontaneously broken in the early universe. We apply two different methods to calculate the gravitational wave spectrum: One is to calculate the gravitational wave spectrum directly from numerical simulations, and another is to calculate it indirectly by estimating the unequal time anisotropic stress power spectrum of the scalar field. Both analysises indicate that the slope of the spectrum changes at two characteristic frequencies corresponding to the Hubble radius at the decay of domain walls and the width of domain walls, and that the spectrum between these two characteristic frequencies becomes flat or slightly red tilted. The second method enables us to evaluate the GW spectrum semi-analytically for the frequencies which can not be resolved in the finite box lattice simulations, but relies on the assumptions for the unequal time correlations of the source.