Simultaneous estimation of astrophysical and cosmological stochastic gravitational-wave backgrounds with terrestrial detectors

TL;DR

This paper discusses methods to distinguish astrophysical and cosmological stochastic gravitational-wave backgrounds using current and future terrestrial detectors, highlighting the potential for third-generation detectors to identify cosmological signals.

Contribution

It introduces a Bayesian framework for simultaneous estimation and upper limits of astrophysical and cosmological gravitational-wave backgrounds, emphasizing the role of source subtraction with advanced detectors.

Findings

Advanced LIGO/Virgo cannot separate sources at design sensitivity.

Third-generation detectors can reduce astrophysical signals through source subtraction.

Potential detection of cosmological signals with Cosmic Explorer and Einstein Telescope.

Abstract

The recent Advanced LIGO and Advanced Virgo joint observing runs have not claimed a stochastic gravitational-wave background detection, but one expects this to change as the sensitivity of the detectors improves. The challenge of claiming a true detection will be immediately succeeded by the difficulty of relating the signal to the sources that contribute to it. In this paper, we consider backgrounds that comprise compact binary coalescences and additional cosmological sources, and we set simultaneous upper limits on these backgrounds. We find that the Advanced LIGO, Advanced Virgo network, operating at design sensitivity, will not allow for separation of the sources we consider. Third generation detectors, sensitive to most individual compact binary mergers, can reduce the astrophysical signal via subtraction of individual sources, and potentially reveal a cosmological background. Our Bayesian analysis shows that, assuming a detector network containing Cosmic Explorer and Einstein Telescope and reasonable levels of individual source subtraction, we can detect cosmological signals $\Omega_{\rm{CS}} (25\,\rm{Hz})=4.5 \times 10^{-13}$ for cosmic strings, and $\Omega_{\rm BPL}(25\,\rm{Hz})= 2.2 \times 10^{-13}$ for a broken power law model of an early universe phase transition.