Searching for the Stochastic Gravitational Wave Background with Advanced Gravitational Wave Detectors

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This award supports research in gravitational waves data analysis and it addresses the priority areas of NSF's "Windows on the Universe" Big Idea. Stochastic gravitational-wave background arises as an incoherent superposition of many gravitational wave signals generated by uncorrelated astrophysical and cosmological sources throughout the universe. Measuring the astrophysical component of this background, for example due to mergers of black holes and/or neutron stars, would provide information about how the structure in the universe formed. Similarly, measuring the cosmological component of this background would provide unique information about the universe when it was a fraction of a second old, and about the physical laws that apply to very high energy scales that are not reproducible in laboratories. This project aims to search and detect the stochastic gravitational wave background using the upcoming Advanced LIGO, Virgo, and Kagra data, as well as to characterize its composition and study implications for different astrophysical and cosmological models. The project will enable involvement of undergraduate and graduate students in frontier research, and it will promote gravitational-wave science to the general public.Stochastic gravitational-wave background (SGWB) arises as an incoherent superposition of many gravitational wave signals generated by uncorrelated astrophysical or cosmological sources throughout the universe. This project aims to search for (and detect) the SGWB using the upcoming aLIGO, aVirgo, and KAGRA data from the fourth observing run (O4) in 2022/23, leveraging the improved detector sensitivities expected for O4 and deploying two search techniques. The traditional cross-correlation based search is expected to be 10 times more sensitive than the most recent results based on the first three observation runs, with another factor of 4 improvement expected with the A+ detector sensitivities in 2024 and beyond. For the specific case of the SGWB due to binary black hole mergers, the full Bayesian Search will be developed with the potential to improve the sensitivity by ~1000 times relative to the cross-correlation search. These searches will probe the high-redshift distribution of the compact binary systems and provide information about their formation and evolution. They will also constrain cosmological SGWB models, such as inflationary, phase transitions, and cosmic (super)string models, and therefore probe the physics of fundamental interactions at very high energies, unachievable in laboratories. Both the cross-correlation and the Bayesian SGWB searches will estimate the directional content of the SGWB, enabling future studies correlating the SGWB with electromagnetic tracers of matter structure in the universe, such as galaxy counts or gravitational lensing. In addition to involving graduate and undergraduate students in frontier research, this project includes a series of activities designed to bring the excitement of the gravitational-wave science to broad communities in the Twin Cities and Minnesota, including physics demonstrations and presentations in K-12 schools and data analysis projects for implementation in K-12 classrooms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.