Stochastic backgrounds of gravitational waves
Michele Maggiore
TL;DR
The paper surveys the rationale for seeking stochastic gravitational-wave backgrounds and systematically builds the framework to connect cosmological signals with detector observables. It defines key quantities such as $\Omega_{\rm gw}(f)$, $S_h(f)$, and $h_c(f)$, and derives how these signals couple to detectors via strain sensitivity, pattern functions, and overlap integrals, highlighting single- and cross-correlation strategies. A central contribution is the explicit presentation of optimal cross-correlation formalisms, including the overlap reduction function $\Gamma(f)$ and the corresponding SNR, alongside practical expressions for the minimum detectable $h_0^2\Omega_{\rm gw}$ for given detector performance. The review also describes current experimental platforms, emphasizing ultracryogenic resonant bars and their narrow-band capabilities, and frames how near-future sensitivities compare with theoretical predictions and existing bounds, guiding search strategies.
Abstract
We review the motivations for the search of stochastic backgrounds of gravitational waves and we compare the experimental sensitivities that can be reached in the near future with the existing bounds and with the theoretical predictions.