Nearly degenerate neutrinos, supersymmetry and radiative corrections

If neutrinos are to play a relevant cosmological role, they must he essenti ally degenerate with a mass matrix of the bimaximal mixing type. We study t his scenario in the MSSM framework, finding that if neutrino masses are pro duced by a see-saw mechanism, the radiative corrections give rise to mass s plittings and mixing angles that can accommodate the atmospheric and the (l arge angle MSW) solar neutrino oscillations. This provides a natural origin for the Delta m(sol)(2) much less than Delta m(atm)(2) hierarchy. On the o ther hand, the vacuum oscillation solution to the solar neutrino problem is always excluded. We discuss also in the SUSY scenario other possible effec ts of radiative corrections involving the new neutrino Yukawa couplings, in cluding implications for triviality limits on the Majorana mass, the infrar ed axed point value of the top Yukawa coupling, and gauge coupling and bott om-tau unification. (C) 2000 Elsevier Science B.V. All rights reserved.