Whispers of Supergravity in Gravitational Wave Backgrounds: Determining the Gravitino Mass from Cosmic Thermal History
Year: 2026
Type: other
Abstract: Gravitino masses above the electroweak scale provide the simplest solution to the gravitino problem, but such large mass scales lie far beyond the reach of collider experiments. We show that the stochastic gravitational wave background offers a direct probe of this otherwise inaccessible regime. Despite decaying before Big-Bang Nucleosynthesis (BBN), these gravitinos naturally generate a period of early matter domination in the early universe. This non-standard epoch leaves a characteristic imprint on any primordial gravitational wave background, characterised by two frequencies corresponding to the onset and end of this phase. We demonstrate that, when early matter domination occurs while the gravitational-wave background is freely propagating, its spectral features enable the direct inference of both the gravitino mass and initial abundance, while more generally, even when the background is sourced during the early matter-dominated epoch, the gravitino mass can still be determined. Future gravitational wave observatories span a vast frequency range, enabling sensitivity to gravitino masses from the BBN bound of $\mathcal{O}(100) \text{TeV}$ up to $\mathcal{O}(10^{10}) \text{TeV}$. Already, the signal reported by NANOGrav, if primordial in origin, offers a potential probe of gravitino masses in the range $500$-$10^4 \text{TeV}$. Gravitational wave observables therefore probe an enormous region of parameter space, far beyond the reach of collider experiments. We are entering an era in which supergravity can be probed through gravitational wave backgrounds alongside collider experiments.
Authors: Spalding, Angus, King, Stephen F.
Institution: University of Southampton
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7162656187