Pseudo-Dirac solar neutrinos

Three of the viable solutions of the solar neutrino problem are consistentwith close to maximal leptonic mixing:$\sin^2\theta_{12}={1\over2}(1-\epsilon_{12})$ with $|\epsilon_{12}|\ll1$.Flavor models can naturally explain close to maximal mixing if approximatehorizontal symmetries force a pseudo-Dirac structure on the neutrino massmatrix. An experimental determination of $|\epsilon_{12}|$ andsign($\epsilon_{12}$) can constrain the structure of the lepton mass matricesand consequently provide stringent tests of such flavor models. If both$|\epsilon_{12}|$ and $\Delta m^2_{21}$ are known, it may be possible toestimate the mass scale of the pseudo-Dirac neutrinos. Radiative corrections toclose to maximal mixing are negligible. Subtleties related to the kinetic termsin Froggatt-Nielsen models are clarified.Comment: 24 pages; v3: significant improvements and modifications, particularly in the three generation analysi