Linear Seesaw for Dirac Neutrinos with $A_4$ Flavour Symmetry

TL;DR

This paper introduces a linear seesaw model with $A_4$ symmetry that naturally explains light Dirac neutrino masses, predicts specific mixing angles and CP phases, and aligns with cosmological bounds.

Contribution

It presents a novel $A_4$-based linear seesaw framework for Dirac neutrinos, predicting hierarchical masses, mixing angles, and CP phases with minimal unwanted terms.

Findings

Predicts normal hierarchical neutrino masses

Leptonic CP phase in specific range including maximal value

Model saturates cosmological neutrino mass bounds

Abstract

We propose a linear seesaw model to realise light Dirac neutrinos within the framework of $A_4$ discrete flavour symmetry. The additional fields and their transformations under the flavour symmetries are chosen in such a way that naturally predicts the hierarchies of different elements of the seesaw mass matrix and also keeps the unwanted terms away. For generic choices of flavon alignments, the model predicts normal hierarchical light neutrino masses with the atmospheric mixing angle in the lower octant. Apart from predicting interesting correlations between different neutrino parameters as well as between neutrino and model parameters, the model also predicts the leptonic Dirac CP phase to lie in a specific range $-\pi/2\lesssim \delta \lesssim -\pi/5$ and $\pi/5\lesssim \delta \lesssim \pi/2$ that includes the currently preferred maximal value. The predictions for the absolute neutrino masses in one specific version of the model can also saturate the cosmological upper bound on sum of absolute neutrino masses.