Compatibility of theta13 and the Type I Seesaw Model with A4 Symmetry

TL;DR

This paper explores how the A4 flavor symmetry constrains neutrino masses and mixing angles within a type I seesaw model, predicting specific correlations and deviations that future experiments can test.

Contribution

It derives formulae linking A4 symmetry parameters to neutrino observables and predicts correlations between theta13 and atmospheric mixing deviations in different hierarchies.

Findings

In the normal hierarchy, a sizable deviation from maximal atmospheric mixing is predicted.

Deviations are negligible in the inverted hierarchy case.

Future measurements can test the predicted correlations and triplet vev patterns.

Abstract

We derive formulae for neutrino masses and mixing angles in a type I seesaw framework with an underlying A4 flavor symmetry. In particular, the Majorana neutrino mass matrix includes contributions from an A4 triplet, 1, 1', and 1" flavon fields. Using these formulae, we constrain the general A4 parameter space using the updated global fits on neutrino mixing angles and mass squared differences, including results from the Daya Bay and RENO experiments, and we find predictive relations among the mixing parameters for certain choices of the triplet vacuum expectation value. In the normal hierarchy case, sizable deviation from maximal atmospheric mixing is predicted, and such deviation is strongly correlated with the value of theta13 in the range of ~ (8-10) degrees. On the other hand, such deviation is negligible and insensitive to theta13 in the inverted mass hierarchy case. We also show expectations for the Dirac CP phase resulting from the parameter scan. Future refined measurements of neutrino mixing angles will test these predicted correlations and potentially show evidence for particular triplet vev patterns.