Two-Step Procedure to Detect Cosmological Gravitational Wave Backgrounds with Next-Generation Terrestrial Gravitational-Wave Detectors

TL;DR

This paper introduces a new method for detecting cosmological gravitational-wave backgrounds with next-generation detectors, effectively separating them from astrophysical foregrounds like binary black holes and neutron stars.

Contribution

The authors develop a two-step Bayesian framework that removes resolved binary signals and jointly infers the cosmological background amidst astrophysical foregrounds.

Findings

Detection at 5 sigma level for _ ext{ref}  2.7 imes 10^{-12} / \u221a{T_ ext{obs}}

Sensitivity within a factor of  2 of ideal case without foregrounds

Method applicable to Cosmic Explorer and Einstein Telescope detectors

Abstract

Cosmological gravitational-wave backgrounds are an exciting science target for next-generation ground-based detectors, as they encode invaluable information about the primordial Universe. However, any such background is expected to be obscured by the astrophysical foreground from compact-binary coalescences. We propose a novel framework to detect a cosmological gravitational-wave background in the presence of binary black holes and binary neutron star signals with next-generation ground-based detectors, including Cosmic Explorer and the Einstein Telescope. Our procedure involves first removing all the individually resolved binary black hole signals by notching them out in the time-frequency domain. Then, we perform joint Bayesian inference on the individually resolved binary neutron star signals, the unresolved binary neutron star foreground, and the cosmological background. For a flat cosmological background, we find that we can claim detection at $5\,\sigma$ level when $\Omega_\mathrm{ref}\geqslant 2.7\times 10^{-12}/\sqrt{T_\mathrm{obs}/\mathrm{yr}}$, where $T_\mathrm{obs}$ is the observation time (in years), which is within a factor of $\lesssim2$ from the sensitivity reached in absence of these astrophysical foregrounds.