Detecting cosmological gravitational waves background after removal of compact binary coalescences in future gravitational wave detectors

TL;DR

This paper explores how removing individually detected compact binary signals can help future gravitational wave detectors identify the primordial cosmological stochastic gravitational wave background, despite the unresolved binary foreground.

Contribution

It demonstrates that time-frequency notching of resolved binary signals can reduce foreground contamination, approaching the sensitivity limit set by unresolved binaries.

Findings

Notching can reach the SGWB sensitivity floor.

Unresolved binaries may limit future SGWB searches.

Sensitivity floor depends on binary coalescence rates.

Abstract

The improved sensitivity of third generation gravitational wave detectors opens the possibility of detecting the primordial cosmological stochastic gravitational wave background (SGWB). Detection of the cosmological SGWB is facing a novel challenge: it will likely be masked by the foreground generated by a large number of coalescences of compact binary systems consisting of black holes and/or neutron stars. In this paper, we investigate the possibility of reducing this foreground by removing (notching) the individually resolved compact binary signals in time-frequency space. We establish that such an approach could be used to reach the SGWB sensitivity floor defined by the unresolved part of the compact binaries foreground, which we find to be between $\Omega_{\rm GW} \sim (9.1 \times10^{-12} - 8.6\times10^{-11})$ for a frequency independent energy density spectrum and depending on the rate of coalescing binary neutron star systems. Since third-generation gravitational wave detectors will not be able to resolve all compact binaries, the unresolvable component of the compact binaries foreground may limit the SGWB searches with these detectors.