Discrete Flavour Symmetries in Light of T2K

TL;DR

This paper demonstrates that discrete flavour symmetries can predict a non-zero theta_13 angle in neutrino mixing, aligning well with experimental data, and provides specific models with concrete predictions for mixing angles and CP violation.

Contribution

It introduces specific discrete flavour symmetry models that predict a non-zero theta_13 and consistent mixing angles, with detailed subgroup choices and resulting parameter values.

Findings

Predicted sin^2 theta_13 = 0.045 for n=4 and 0.011 for n=8.

Theta_23 and theta_12 close to experimental best fits, especially for n=8.

CP phase delta_CP predicted to be 0 or pi, indicating CP conservation.

Abstract

We show that a non-vanishing angle theta_13 of order 0.1 can be predicted in the framework of discrete flavour symmetries. We assume that left-handed leptons transform as triplets under a group G_f which is broken in such a way that neutrino and charged lepton sectors remain invariant under the subgroups G_nu and G_e of G_f, respectively. In this limit mixing angles and the Dirac CP violating phase delta_CP are determined. By choosing G_f=Delta(6 n^2) (n=4,8), G_nu=Z_2 x Z_2 and G_e=Z_3 we find sin^2 theta_13=0.045(0.011) for n=4(8). At the same time theta_23 and theta_12 remain close to their experimental best fit values, particularly in the case n=8, where sin^2 theta_23 = 0.424 and sin^2 theta_12 = 0.337. delta_CP is predicted to be 0 or pi so that CP is conserved in our examples.