GUT models

I emphasize that a grand unified theory (GUT) based on the minimal supersymmetric SO(10) remains a possibility in nature. The Yukawa couplings of the third generation fermions can all unify to a point provided strong constraints are placed on the supersymmetric (SUSY) parameters entering the analysis via the low-energy SUSY threshold corrections. This makes the minimal SO(10) a very predictive and testable GUT. In the second part of the paper the focus is on the relation between the neutrino masses, SUSY and lepton flavour violation. In a class of GUT models, the large atmospheric mixing angle induces significant τ → μγ branching ratio. This can be tested in present experiments. Chances are that the lepton flavour violation in τ decay will become the first signal of new physics observed at B factories