Soft A 4 → Z 3 symmetry breaking and cobimaximal neutrino mixing

摘要

I propose a model of radiative charged-lepton and neutrino masses with A 4 symmetry. The soft breaking of A 4 to Z 3 lepton triality is accomplished by dimension-three terms. The breaking of Z 3 by dimension-two terms allows cobimaximal neutrino mixing ( θ 13 ≠ 0 , θ 23 = π / 4 , δ CP = ± π / 2 ) to be realized with only very small finite calculable deviations from the residual Z 3 lepton triality. This construction solves a long-standing technical problem inherent in renormalizable A 4 models since their inception.