A likely source of a gravitational-wave background (GWB) in the frequency band of the Advanced LIGO, Virgo and KAGRA detectors is the superposition of signals from the population of unresolvable stellar-mass binary-black-hole (BBH) mergers throughout the Universe. Since the duration of a BBH merger in band (∼1 s) is much shorter than the expected separation between neighboring mergers (∼10^3 s), the observed signal will be “popcorn-like” or intermittent with duty cycles of order 10^{−3}. This background is best described by a Gaussian mixture-model, which includes a duty cycle parameter that quantifies the degree of intermittence. We propose a stochastic-signal-based search for the GWB from subthreshold BBH mergers. While the development of this search is ongoing, results thus far are very promising that our search will perform much better than the standard search used in stochastic gravitational-wave data analysis. |