Phenomenology in the Zee Model with the A_4 Symmetry

TL;DR

This paper extends the Zee model with A_4 symmetry to explain neutrino masses and mixing, predicting specific mass sum rules, effective neutrinoless double beta decay mass, and potential collider signatures.

Contribution

It introduces a softly broken A_4 symmetry into the Zee model, leading to tribimaximal mixing and new predictions for neutrino mass parameters and collider phenomenology.

Findings

Compatible with tribimaximal mixing and neutrino oscillation data.

Predicts a lower bound on neutrinoless double beta decay effective mass.

Suggests charged Higgs bosons could be light enough for LHC detection.

Abstract

The Zee model generates neutrino masses at the one-loop level by adding charged SU(2)_L-singlet and extra SU(2)_L-doublet scalars to the standard model of particle physics. As the origin of the nontrivial structure of the lepton flavor mixing, we introduce the softly broken A_4 symmetry to the Zee model. This model is compatible with the tribimaximal mixing which agrees well with neutrino oscillation measurements. Then, a sum rule m_1 e^{i alpha_12} + 2 m_2 + 3 m_3 e^{i alpha_32} = 0 is obtained and it results in Delta m^2_31 < 0 and m_3 > 1.8*10^{-2}eV. The effective mass |(M_nu)_{ee}| for the neutrinoless double beta decay is predicted as | (M_\nu)_{ee} | > 1.7*10^{-2}eV. The characteristic particles in this model are SU(2)_L-singlet charged Higgs bosons s^+_alpha (alpha=xi,eta,zeta) which are made from a 3-representation of A_4. Contributions of s^+_alpha to the lepton flavor violating decays of charged leptons are almost forbidden by an approximately remaining Z_3 symmetry; only BR(tau to ebar mu mu) can be sizable by the flavor changing neutral current interaction with SU(2)_L-doublet scalars. Therefore, s^+_alpha can be easily light enough to be discovered at the LHC with satisfying current constraints. The flavor structures of BR(s^-_alpha to ell nu) are also discussed.