Neutrino masses, mixing angles and the unification of couplings in the MSSM

In the light of the gathering evidence for nu(mu)-nu(tau) neutrino oscillat ions, coming in particular from the Super-Kamiokande data on atmospheric ne utrinos, we re-analyze the unification of gauge and Yukawa couplings within the minimal supersymmetric extension of the Standard Model (MSSM). Guided by a range of different grand-unified models, we stress the relevance of la rge mixing in the lepton sector for the question of bottom-tau Yukawa coupl ing unification. We also discuss the dependence of the favoured value of ta n beta on the characteristics of the high-energy quark and lepton mass matr ices. In particular, we find that, in the presence of large lepton mixing, Yukawa unification can be achieved for intermediate Values of tan beta that were previously disfavoured. The renormalization-group sensitivity to the structures of different mass matrices may enable Yukawa unification to serv e as a useful probe of GUT models.