Neutrino mixing and flavour changing processes

We study the implications of a large nu(mu) - nu(tau) mixing angle on flavour changing transitions of quarks and leptons in supersymmetric extensions of the standard model. Two patterns of supersymmetry breaking are considered, models with modular invariance and the standard scenario of universal soft breaking terms at the GUT scale. The analysis is performed for two symmetry groups G x U(1)(F), with G = SU(5) and G = SU(3)(3), where U(1)(F) is a family symmetry. Models with modular invariance are in agreement with observations only for restricted scalar quark and gaugino masses, (M) over bar(q)(2)/m((g) over bar)(2) similar or equal to 7 /9 and m((b) over bar) > 350 GeV. A characteristic feature of models with large tan beta and radiatively induced flavour mixing is a large branching ratio for mu --> e gamma. For both symmetry groups and for the considered range of supersymmetry breaking mass parameters we find BR(mu --> e gamma) > 10(-14) (C) 2000 Elsevier Science B.V. All rights reserved.