Textures for atmospheric and solar neutrino oscillations

Abstract

A large θ μτ mixing angle, together with hierarchies in the neutrino Δ m 2 and in the charged lepton masses, place a significant restriction on the textures of the lepton mass matrices. In theories with three light neutrinos, a simple hypothesis leads to a complete list of four zeroth-order textures for lepton mass matrices is found: three for neutrinos which naturally yield θ μτ ≈1 with vanishing θ eτ and Δ m 2 ⊙, and one for charged leptons which naturally yields θ μτ ≈1 with m e = m μ = θ eτ =0. These textures provide suitable starting points for constructing theories which account for both atmospheric and solar neutrino fluxes. Using flavor symmetries, two schemes for such lepton masses are found, and example constructions exhibited.