Can gravitational waves reveal the mass of invisible particles from the early universe?

Supergravity predicts massive gravitinos that decay before the universe was one second old, but their lingering effects reshape the early cosmos. These particles trigger a distinct period of matter domination that imprints two characteristic frequencies onto any primordial gravitational wave background. By measuring these frequencies with next-generation wave detectors, astronomers could pinpoint gravitino masses up to 10 billion TeV—far beyond collider reach.