The unresolved stochastic background from compact binary mergers detectable by next-generation ground-based gravitational-wave observatories

TL;DR

Next-generation ground-based gravitational-wave detectors will face significant astrophysical backgrounds from unresolved compact binary mergers, which could hinder the detection of primordial cosmological signals, necessitating advanced data analysis techniques.

Contribution

This paper provides a data-driven estimate of the unresolved CBC background for next-generation detectors, incorporating statistical and systematic errors to inform detector design and data analysis.

Findings

Unresolvable CBC background is a major noise source for future detectors.

The estimated background could significantly impede detection of cosmological signals.

Advanced inference methods are needed to distinguish cosmological backgrounds from astrophysical noise.

Abstract

The next generation of ground-based gravitational-wave detectors will look much deeper into the Universe and have unprecedented sensitivities and low-frequency capabilities. Especially alluring is the possibility of detecting an early-Universe cosmological stochastic background that could provide important insights into the beginnings of our Universe and fundamental physics at extremely high energies. However, even if next-generation detectors are sensitive to cosmological stochastic backgrounds, they will be masked by more dominant astrophysical backgrounds, namely the residual background from the imperfect subtraction of resolvable compact binary coalescences (CBCs) as well as the CBC background from individually unresolvable CBCs. Using our latest knowledge of masses, rates, and delay time distributions, we present a data-driven estimate of the unresolvable CBC background that will be seen by next-generation detectors. Accounting for statistical and systematic errors, this estimate quantifies an important piece in the CBC noise budget for next-generation detectors and can help inform detector design and subtraction algorithms. We compare our results with predictions for backgrounds from several cosmological sources in the literature, finding that the unresolvable background will likely be a significant impediment for many models. This motivates the need for simultaneous inference methods or other statistical techniques to detect early-Universe cosmological backgrounds.