Relating small neutrino masses and mixing

Experiments on neutrino oscillations have uncovered several small parameters, $θ_{13}$ being a prominent one. Others are the solar mass splitting {\em vis-à-vis} the atmospheric one and the deviation of $θ_{23}$ from maximal mixing. In this talk we elaborate on a neutrino mass model based on the see-saw mechanism in which the mixing angles to start with are either vanishing ($θ_{13}$ and $θ_{12}$) or $π/4$ ($θ_{23}$). The atmospheric mass splitting is taken as a part of this initial structure but the solar splitting is absent. A perturbative contribution, originating from a Type-I see-saw, results in non-zero values of $θ_{13}$, $θ_{12}$, $Δm^2_{solar}$, and shifts $θ_{23}$ slightly from $π/4$, interrelating them all. The model incorporates CP-violation, the phase $δ$ being close to 3$π$/2 for (a) quasi-degeneracy or (b) inverted mass ordering. It will be put to test as the neutrino parameters get better determined.

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