Large anisotropies of the stochastic gravitational wave background from cosmic domain walls

TL;DR

This paper explores how quantum fluctuations during inflation cause large anisotropies in the stochastic gravitational wave background from cosmic domain walls, potentially detectable by future GW observatories.

Contribution

It introduces a mechanism linking inflationary quantum fluctuations to observable anisotropies in the SGWB from cosmic domain walls, providing a new way to probe inflation.

Findings

Angular power spectrum of anisotropies is scale-invariant and exceeds 10^{-2}

Anisotropies could be detected by future gravitational-wave detectors

SGWB anisotropies can help verify inflation models and energy scales

Abstract

We investigate the stochastic gravitational wave background (SGWB) from cosmic domain walls (DWs) caused by quantum fluctuations of a light scalar field $\phi$ during inflation. Perturbations of $\phi$ remain almost constant after leaving the Hubble horizon. The probabilities of the two domains depend on the averaged value of $\phi$ at each large scale region, leading to large scale perturbations of DW energy density and large anisotropies in the SGWB. We find that the angular power spectrum is scale-invariant and at least of the order of $10^{-2}$, which is expected to be detected by future gravitational-wave (GW) detectors. Since we have not detected primordial GWs yet, anisotropies of the SGWB could help us to verify the rationality of inflation and determine the energy scale of inflation.