Two categories of approximately μ-τ symmetric neutrino mass textures

We present ten phenomenologically viable neutrino mass textures, which are approximately mu-tau symmetric: two for the normal mass hierarchy, three for the inverted mass hierarchy, and five for the quasi-degenerate mass pattern. Each texture falls into two categories characterized by either sin theta(13) -> 0 (referred to as (C1)), or sin theta(12) -> 0 (referred to as (C2)) in the mu-tau symmetric limit, where theta(12) and theta(13), respectively, stand for the nu(e)-nu(mu) and nu(e)-nu(tau) mixing angles. Our textures that depend on the signs of neutrino masses as well as on (C1) and (C2) are so constructed to satisfy general relations, which ensure that Delta m(circle dot)(2)/Delta m(atm)(2) ( R) << 1 and sin(2)theta(13) << 1, where Delta m(circle dot)(2)/Delta m(atm)(2) are neutrino mass differences squared, respectively, for solar and atmospheric neutrinos. Three textures are found to provide R similar to sin(2)theta(13). (c) 2007 Elsevier B.V. All rights reserved.