Pseudo-Dirac Solar Neutrinos

Abstract

Three of the viable solutions of the solar neutrino problem are consistent with close to maximal leptonic mixing: ${\sin }^2{\theta }_{12}=\frac{1}{2}(1-{ϵ}_{12})$ with $|{ϵ}_{12}|\ll 1$. 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 $\Delta m_{21}^2$ 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.

Comments: 24 pages; v3: significant improvements and modifications, particularly in the three generation analysis