Two-Step Procedure to Detect Cosmological Gravitational Wave Backgrounds with Next-Generation Terrestrial Gravitational-Wave 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 $5\ddot{I}ƒ$ level when $\hat{I}{\text{c◯}}_{\mathrm{ref}}⩾2.7\times 10^{-12}/\sqrt{T_{\mathrm{obs}}/\mathrm{yr}}$, where $T_{\mathrm{obs}}$ is the observation time (in years), which is within a factor of $\lesssim 2$ from the sensitivity reached in absence of these astrophysical foregrounds.

Main text: 7 pages, 3 figures, 1 table. Supplemental material: 12 pages, 9 figures, 1 table