A New Type of Complex Neutrino Mass Texture and mu-tau Symmetry

Abstract

Relying upon the usefulness of the μ-τsymmetry, we find a new type of neutrino mass texture with a single phase parameter δthat describes maximal atmospheric neutrino mixing and Dirac CP violation due to the presence of δ. The Majorana phase associated with the third massive neutrino turns out to be identical to the Dirac phase while other Majorana phases vanish. The nonvanishing reactor neutrino mixing angle θ_{13} is induced by a μ-τsymmetry breaking effect. Flavor neutrino masses that supply the μ-τsymmetry breaking terms become pure imaginary for δ=\pm π/2, leading to maximal CP violation. There is a parameter denoted by η, which is either O(\sqrt{Δm^2_\odot/Δm^2_{atm}}) in the normal mass hierarchy, or O(Δm^2_\odot/Δm^2_{atm}) in the inverted mass hierarchy. In the inverted mass hierarchy, the contribution of O(\sin^2θ_{13}) is found to be significant and cannot be neglected. Our texture also leads to quasi degenerate neutrinos with masses of O(\sqrt{Δm^2_{atm}}), which serves as the scale for the effective neutrino mass in (ββ)_{0ν}-decay. This texture does not include η, and Δm^2_\odot naturally arises from contributions of O(\sin^2θ_{13}) to give Δm^2_\odot/Δm^2_{atm}\sim\sin^2θ_{13}, yielding the prediction of \sin^2θ_{13}=O(10^{-2}).