Gravitational Wave Signatures of Low-Scale Seesaw Mechanism for Neutrinos

Neutrinos are the most elusive particles of the Standard Model. The mechanism responsible for their mass generation remains unknown and requires introducing new hypothetical particles and interactions. Usually, a very high mass scale is considered for this new physics, making it difficult to probe such scenarios in conventional particle physics experiments. Surprisingly, this high-scale seesaw framework can be tested in gravitational wave experiments by searching for a flat spectrum from the dynamics of cosmic strings, however, the signal is rather generic across many high-scale seesaw models. I will consider the possibility of having a low-scale seesaw mechanism generating neutrino masses within a framework of a model with gauged lepton number. In this case the gravitational wave signal arises from a first order phase transition in the early Universe, leading to a peak structure in the gravitational wave spectrum. The results presented are relevant for upcoming gravitational wave experiments, such as LISA, DECIGO, and Big Bang Observer. I will also discuss whether this scenario can explain the recent signal detected by the NANOGrav experiment.