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 ver-sion it is the presence of the right-handed neutrino that is responsible for it. In renormalizable grand unied 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 Yukawa unication with the large atmospheric neutrino mixing angle in the context of a SO(10) grand unied theory. Also, a t to the available low energy masses and mixings points to-wards the domination of this non-canonical contribution with respect to the canonical one. Finally I will explicitly present the minimal supersymmetric SO(10) model with all the above nice features.