Majorana mass generation, gravitational waves and cosmological tensions

TL;DR

This paper explores how neutrino Majorana mass generation in the early universe could produce detectable gravitational waves, potentially addressing cosmological tensions and contributing to signals observed by NANOGrav.

Contribution

It introduces a model linking neutrino mass generation to gravitational wave backgrounds and cosmological tensions, highlighting the split seesaw model's implications.

Findings

Primordial gravitational waves could originate from phase transitions and cosmic strings.

Low-scale Majorana mass generation may resolve primordial deuterium issues.

The model predicts a subdominant GW signal consistent with NANOGrav observations.

Abstract

A neutrino Majorana mass generation in the early universe might have left imprints in cosmological observables. It can source the production of a detectable stochastic background of primordial gravitational waves with a spectrum that combines a contribution from a first order phase transition production and from the vibration of global cosmic strings. An intriguing possibility is given by the split seesaw model. In this case, in addition to the traditional high scale seesaw, a low scale neutrino Majorana mass generation can solve a potential primordial deuterium problem and ameliorate the cosmological tensions of the $\Lambda$CDM model. At the same time, it can also produce subdominant contribution to the NANOGrav signal of a stochastic background of gravitational waves (GWs), in addition to the astrophysical dominant contribution from supermassive black hole mergers.