Dr Arianna Renzini (University of Milan-Bicocca)

Gravitational-wave backgrounds (GWBs) encompass a multitude of signals across the wide gravitational-wave (GW) frequency spectrum, and represent key targets in the panorama of gravitational-wave data analysis. Typically, GWBs are considered to be the collection of GW signals that lie just beneath the threshold of detection. In this talk, I will broadly introduce GWBs and various ongoing or near-future detection efforts, focusing on ground-based interferometers such as LIGO and Virgo. I will specifically focus on the astrophysical GWB from binary black holes and neutron stars, as it is expected to be the main background source in the LIGO-Virgo-KAGRA (LVK) frequency range. I will describe the flagship LVK GWB searches and outline their key implications beyond GWs: The GWB power spectrum includes information on binary formation history and mass distribution, while its angular power spectrum is a tracer of large-scale structure, and many other potential sky distributions. I will present two new and improved GWB searches I am involved in, which are expected to outperform current approaches and which we plan to apply to O4 data. Finally, I will close with an overview of the future of GWBs with promising new detectors such as LISA and 3G interferometers.