Realizing Tri-bimaximal Mixing in Minimal Seesaw Model with S4 Family Symmetry

TL;DR

This paper constructs a minimal seesaw model with S4 symmetry that naturally produces tri-bimaximal neutrino mixing, with small corrections, and predicts a normal hierarchy with specific mass parameters.

Contribution

It presents a minimal seesaw model with S4 symmetry that achieves exact tri-bimaximal mixing at leading order and includes detailed scalar VEV alignment mechanisms.

Findings

Light neutrino mass spectrum has normal hierarchy with m_1=0.

Predicted sum of neutrino masses is about 0.058 eV.

Effective Majorana mass |m_ee| is approximately 0.003 eV.

Abstract

In this paper, we realize the tri-bimaximal mixing in the lepton sector in the context of minimal seesaw in which only two right-handed neutrinos are introduced, with the discrete group $S4$ as the family symmetry. In order to constrain the form of superpotential, a $Z3$ symmetry is also introduced. In the model, the mass matrices for charged leptons and right-handed neutrinos are diagonal. The unitary matrix that diagonalizes the light Majorana neutrino mass matrix is exact tri-bimaximal at LO, and is corrected by small quantities of $\mathcal{O}(0.01)$ at NLO. The mechanism to get the particular scalar VEV alignments used is also presented. Phenomenologically, the mass spectrum is of normal hierarchy with $m_1=0$, and $\sum m_i$ and $|m_{ee}|$ are about $0.058 eV$ and $0.003 eV$ respectively.