Neutrino mixing and see-saw mechanism

Abstract

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

Comments: Latex, 7 pages; added: new references, a paragraph (Note added) on bi-maximal mixing and double beta decay; footnotes changed