Abstract
Detection of primordial gravitational-wave backgrounds generated during the early universe phase transitions is a key science goal for future ground-based detectors. The rate of compact binary mergers is so large that their cosmological population produces a confusion background that could masquerade the detection of potential primordial stochastic backgrounds. In this paper we study the ability of current and future detectors to resolve the confusion background to reveal interesting primordial backgrounds. The current detector network of LIGO and Virgo and the upcoming KAGRA and LIGO-India will not be able to resolve the cosmological compact binary source population and its sensitivity to stochastic background will be limited by the confusion background of these sources. We find that a network of three (and five) third generation (3G) detectors of Cosmic Explorer and Einstein Telescope will resolve the confusion background produced by binary black holes leaving only about 0.013\% (respectively, 0.00075\%) unresolved; in contrast, as many as 25\% (respectively, 7.7\%) of binary neutron star sources remain unresolved. Consequently, the binary black hole population will likely not limit observation of primordial backgrounds but the binary neutron star population will limit the sensitivity of 3G detectors to $\Omega_{\rm GW} \sim 10^{-11}$ at 10 Hz (respectively, $\Omega_{\rm GW} \sim 3\times 10^{-12}$).
Highlights
With the continued detections of gravitational waves from binary black hole mergers [1,2,3,4,5,6] and binary neutron star inspirals [7,8], the LIGO Scientific and Virgo Collaborations have kept up to their promise of taking us into an era of gravitational-wave astronomy
We find that a network of three third generation (3G) detectors of Cosmic Explorer and Einstein Telescope will resolve the confusion background produced by binary black holes leaving only about 1.3% unresolved; in contrast, as many as 25% of binary neutron star sources remain unresolved
Where Ωcbc; rec is the background from the recovered compact binary coalescences (CBC) sources that we can subtract from our data, Ωerror is the background because of the error introduced from such a subtraction, Ωcbc; unres is the background from the unresolved CBC sources which are not detected as foreground events
Summary
With the continued detections of gravitational waves from binary black hole mergers [1,2,3,4,5,6] and binary neutron star inspirals [7,8], the LIGO Scientific and Virgo Collaborations have kept up to their promise of taking us into an era of gravitational-wave astronomy In addition to these loud and nearby sources that are seen as isolated transient events, there is a population of weak, unresolved sources at higher redshifts [9,10,11,12,13]. We explore the possibility of probing the cosmological gravitational-wave background with the third generation detectors, after removing the astrophysical background from compact binary mergers from the data.
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