Underlying A4 symmetry for the neutrino mass matrix and the quark mixing matrix

TLDR

A4 symmetry at high energy yields three degenerate neutrino masses while preserving the charged‑lepton mass hierarchy. Radiative corrections in softly broken supersymmetry generate realistic neutrino mixing angles (one maximal, others large) and correct mass splittings, while a similar mechanism yields a calculable quark mixing matrix. The model predicts an imaginary Ue3, implying maximal CP violation in neutrino oscillations, and anticipates observable neutrinoless double‑beta decay and τ→μγ rates.

Abstract

The discrete non-Abelian symmetry A4, valid at some high-energy scale, naturally leads to three degenerate neutrino masses, without spoiling the hierarchy of charged-lepton masses. Realistic neutrino mixing angles (one of which is necessarily maximal and the other large) are then automatically induced radiatively, and the correct mass splittings may be obtained in the context of softly broken supersymmetry. The quark mixing matrix is also calculable in a similar way. The mixing parameter Ue3 is predicted to be imaginary, leading to maximal CP violation in neutrino oscillations. Neutrinoless double beta decay and τ→μγ should be in the experimentally accessible range.