Pseudo-Dirac Solar Neutrinos

Three of the viable solutions of the solar neutrino problem are consistent with close to maximal leptonic mixing: $\sin^2θ_{12}={1\over2}(1-ε_{12})$ with $|ε_{12}|\ll1$. Flavor models can naturally explain close to maximal mixing if approximate horizontal symmetries force a pseudo-Dirac structure on the neutrino mass matrix. An experimental determination of $|ε_{12}|$ and sign($ε_{12}$) can constrain the structure of the lepton mass matrices and consequently provide stringent tests of such flavor models. If both $|ε_{12}|$ and $Δm^2_{21}$ are known, it may be possible to estimate the mass scale of the pseudo-Dirac neutrinos. Radiative corrections to close to maximal mixing are negligible. Subtleties related to the kinetic terms in Froggatt-Nielsen models are clarified.

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