Gravitational Waves in an A4 Neutrino Mass Model

TL;DR

This paper introduces a new A4 and Z4 symmetric neutrino mass model that naturally resolves domain wall issues and predicts a gravitational wave signal detectable by future experiments, aligning with Pulsar Timing Array observations.

Contribution

It presents a novel A4 and Z4 invariant model that enables domain wall annihilation and predicts observable gravitational waves, advancing neutrino physics and cosmology.

Findings

Predicts a gravitational wave signal detectable by future experiments.

Provides a mechanism for domain wall annihilation without explicit symmetry breaking.

Aligns with Pulsar Timing Array gravitational wave observations.

Abstract

The A4 flavor symmetry has provided tremendous insight into the flavor structure of the lepton sector of the Standard Model, predicting a very good approximation to neutrino mixing angles, Tri-Bimaximal Mixing. A4 is spontaneously broken by a scalar called the flavon, and when this happens a number of degenerate vacua can form, resulting in so-called domain walls. These objects are not observed and hence need to be annihilated. This is usually done by explicitly breaking A4 by adding a bias term to the scalar potential. In this paper, we construct a new model invariant under A4 and Z4, which creates cosmologically viable domain walls, lifts the degeneracy of the vacuum giving a natural mechanism for domain walls to annihilate, as well as predicts realistic neutrino mixing angles; all utilizing cross couplings between flavons. The annihilation of the domain walls, with proper choice of wall tension and the consequent bias term, leads to a gravitational wave signal that is potentially detectable in near future gravitational wave experiments, and interestingly intersects with the observed Pulsar Timing Array signal.