The Problem of Neutrino Masses in Extensions of the Standard Model (original) (raw)

We review the problem of neutrino masses and mixings in the context of Grand Unified Theories. After a brief summary of the present experimental status of neutrino physics, we describe how the seesaw mechanism can automatically account for the large atmospheric mixing angle. We provide two specific examples where this possibility is realized by means of a flavour symmetry. We then review in some detail the various severe problems which plague minimal GUT models (like the doublettriplet splitting and proton-decay) and which force to investigate the possibility of constructing more elaborate but realistic models. We then show an example of a quasi-realistic SUSY SU(5) model which, by exploiting the crucial presence of an abelian flavour symmetry, does not require any fine-tuning and predicts a satisfactory phenomenology with respect to coupling unification, fermion masses and mixings and bounds from proton decay.