Neutrino mixing and see-saw mechanism

Abstract

Models of neutrino masses are discussed capable of explaining in a natural way the maximal mixing between $ν_μ$ and $ν_τ$ observed by the Super-Kamiokande collaboration. For three generations of leptons two classes of such models are found implying: a) $Δ{m_{23}}^2 \ll Δ{m_{12}}^2 \approx Δ{m_{13}}^2 $ and a small mixing between $ν_{e}$ and the other two neutrinos, b) $Δ{m_{12}}^2 \ll Δ{m_{13}}^2 \approx Δ{m_{23}}^2$ and a nearly maximal mixing for solar neutrino oscillations in vacuum.