Neutrinos and structure of the intermediate mass scale

Neutrino data lead via the see-saw mechanism to masses of the right handed neutrinos at the intermediate mass scale. A simple formalism is suggested which incorporates the quark-lepton symmetry and allows one to find properties of the intermediate scale (masses and mixing) from neutrino data. The averaged mass scale and the mass hierarchy parameter are introduced and fixed by the data. They determine natural ranges of masses and mixing at the intermediate scale. In particular, a scenario which includes the MSW solution of the solar neutrino problem and tau neutrino as the hot component of the dark matter in the Universe leads to M(2) = (2-4) x 10(10) GeV and M(3) = (4-8) x 10(12) GeV in agreement with the linear mass hierarchy. Strong deviations from these natural ranges imply fine tuning of parameters or/and certain symmetry of the Majorana mass matrix of the right handed neutrinos.