Probing the Neutrino Seesaw Scale with Gravitational Waves

TL;DR

This paper explores how low-scale seesaw models for neutrino masses can produce distinctive gravitational wave signals from early Universe phase transitions and domain wall annihilations, potentially detectable by future experiments.

Contribution

It introduces a low-scale PeV seesaw model with gauged U(1) lepton number that predicts a unique double-peaked gravitational wave spectrum from phase transitions and domain walls.

Findings

Double-peaked gravitational wave spectrum predicted

Signals detectable by upcoming gravitational wave experiments

Links neutrino mass models to observable cosmological signatures

Abstract

Neutrinos are the most elusive particles of the Standard Model. The physics behind their masses remains unknown and requires introducing new particles and interactions. An elegant solution to this problem is provided by the seesaw mechanism. Typically considered at a high scale, it is potentially testable in gravitational wave experiments by searching for a spectrum from cosmic strings, which offers a rather generic signature across many high-scale seesaw models. Here we consider the possibility of a low-scale seesaw mechanism at the PeV scale, generating neutrino masses within the framework of a model with gauged U(1) lepton number. In this case, the gravitational wave signal at high frequencies arises from a first order phase transition in the early Universe, whereas at low frequencies it is generated by domain wall annihilation, leading to a double-peaked structure in the gravitational wave spectrum. The signals discussed here can be searched for in upcoming experiments, including gravitational wave interferometers, pulsar timing arrays, and astrometry observations.