A new study proposes that the stochastic gravitational wave background (SGWB) could be a direct tool to determine the mass of the gravitino, a key hypothetical particle in supergravity theories. This proposal is particularly relevant for gravitino masses above the electroweak scale, a range inaccessible to current collider experiments. The existence of heavy gravitinos in the early universe, even if they decay before Big Bang nucleosynthesis (BBN), would generate an early matter-dominated phase that would leave a distinct imprint on the primordial SGWB.

This imprint would manifest as two characteristic frequencies in the gravitational wave spectrum, corresponding to the beginning and end of this matter-dominated phase. Researchers have shown that these features can be used to directly infer both the gravitino's mass and its initial abundance. The ability of future gravitational wave observatories to cover a wide range of frequencies would allow probing gravitino masses from the BBN limit, on the order of 100 TeV, up to 10^10 TeV. This opens an unprecedented observational window for supergravity.

Recent results from NANOGrav, which have already detected a gravitational wave background signal, are beginning to explore gravitino masses in the range of 500 to 10^4 TeV. This demonstrates the potential of this new methodology to explore a vast region of the supergravity parameter space, far beyond what particle accelerator experiments can achieve. We are entering an era where supergravity can be investigated not only by colliders but also through the gravitational wave background, offering a complementary and powerful avenue for understanding physics beyond the Standard Model.