Collider test of nano-Hertz gravitational waves from pulsar timing arrays

A cosmic first-order phase transition occurring at the MeV scale provides an attractive explanation for the nano-Hertz gravitational wave (GW) background, which is indicated by the recent pulsar timing array data from the NANOGrav, CPTA, EPTA, and PPTA Collaborations. We propose this explanation can be further tested at the colliders if the hidden sector couples to the Standard Model sector via the Higgs portal. Through a careful analysis of the thermal history in the hidden sector, we demonstrate that in order to explain the observed GW signal, the portal coupling must be sizable so that it can be probed through Higgs invisible decay at the LHC or future lepton colliders such as CEPC, ILC, and FCC-ee. Our research offers a promising avenue to uncover the physical origin of the nano-Hertz GWs through particle physics experiments.