Partial $\mu-\tau$ symmetry from kinetic normalization

TL;DR

This paper explores how higher-dimensional operators affecting lepton kinetic terms can lead to partial mu-tau symmetry breaking, significantly constraining the neutrino mass structure and mixing angles, especially in the normal hierarchy.

Contribution

It introduces a novel approach to mu-tau symmetry breaking via kinetic normalization, analyzing its impact on neutrino mass matrices and mixing parameters.

Findings

Normal hierarchy region is highly restricted with second octant atmospheric mixing.

Inverted hierarchy allows a broader range of parameters.

Allowed lightest neutrino mass region is tightly constrained in the normal hierarchy.

Abstract

We consider models with broken $\mu$-$\tau$ permutation symmetry through higher dimensional operators renormalizing the lepton kinetic terms in the action. We study the consequences on the structure of the neutrino mass matrix and find in particular that the allowed region for the lightest mass in the normal hierarchy plotted as a function of the atmospheric mixing element $|V_{\mu3}|$ is very restricted with the atmospheric mixing angle $\theta_{23}$ to lie in the second octant. On the other hand, the corresponding allowed region in the inverted hierarchy regime is less restrictive.