Neutrino masses and mixing in A5 with flavor antisymmetry

We discuss the consequences of assuming that the (Majorana) neutrino mass matrix Mν and the charged lepton mass matrix Ml satisfy STνMνSν=−Mν and T†lMlM†lTl=MlM†l with respect to some discrete groups Sν and Tl contained in A5. These assumptions lead to a neutrino mass spectrum with two degenerate and one massless neutrino and also constrain mixing among them. We derive possible mixing patterns following from the choices Sν=Z2, Z2×Z2, and Tl=Z2,Z2×Z2,Z3,Z5 as subgroups of A5. One predicts the maximal atmospheric neutrino mixing angle θ23 and μ−τ reflection symmetry in a large number of cases, but it is also possible to obtain nonmaximal values for θ23. Only the third column of the neutrino mixing matrix can be obtained at the leading order due to degeneracy in masses of two of the neutrinos. We take up a specific example within the A5 group and identify Higgs vacuum expectation values which realize the above assumptions. Nonleading terms present in this example are shown to lead to splitting among degenerate pairs and a consistent description of both neutrino masses and mixing angles.by Anjan S. Joshipura and Newton Nat