Relatively large theta13 and nearly maximal theta23 from the approximate S3 symmetry of lepton mass matrices

TL;DR

This paper explores how applying the S_3 permutation symmetry to lepton mass matrices, with a specific symmetry-breaking scheme, can naturally produce large theta13 and nearly maximal theta23 neutrino mixing angles, aligning with experimental data.

Contribution

It introduces a two-stage symmetry-breaking scheme in S_3 symmetry that successfully explains large theta13 and theta23 angles in neutrino mixing, which previous models could not achieve.

Findings

Large theta13 (~9°) compatible with T2K results

Maximal theta23 (~45°) achieved in the model

Solar angle theta12 (~34°) consistent with data

Abstract

We apply the permutation symmetry S_3 to both charged-lepton and neutrino mass matrices, and suggest a useful symmetry-breaking scheme, in which the flavor symmetry is explicitly broken down via S_3 -> Z_3 -> nothing in the charged-lepton sector and via S_3 -> Z_2 -> nothing in the neutrino sector. Such a two-stage breaking scenario is reasonable in the sense that both Z_3 and Z_2 are the subgroups of S_3, while Z_3 and Z_2 only have a trivial subgroup. In this scenario, we can obtain a relatively large value of the smallest neutrino mixing angle, e.g., theta_{13} ~ 9^\circ, which is compatible with the recent result from T2K experiment and will be precisely measured in the ongoing Double Chooz and Daya Bay reactor neutrino experiments. Moreover, the maximal atmospheric mixing angle theta_{23} ~ 45^\circ can also be obtained while the best-fit value of solar mixing angle theta_{12} ~ 34^\circ is assumed, which cannot be achieved in previous S_3 symmetry models.