Seesaw, SUSY and SO(10)

The seesaw mechanism can explain why the neutrino masses are so tiny with respect to the charged fermion masses. In the canonical version it is the presence of the right-handed neutrino that is responsible for it. In renormalizable grand unified theories with left-right gauge symmetry it is possible to show quite generically that there is another type of seesaw contribution, mediated by a heavy weak triplet. In this talk I will show that such non-canonical seesaw mechanism can very nicely connect b - τ Yukawa unification with the large atmospheric neutrino mixing angle in the context of a SO(10) grand unified theory. Also, a fit to the available low energy masses and mixings points towards the domination of this non-canonical contribution with respect to the canonical one. Finally I will explicitly present the minimal supersymmetric SO(10) model which has all the above nice features.