FERMION MASSES AND MIXINGS IN SO(10) .2. PROBING GRAND UNIFICATION THROUGH NEUTRINO OSCILLATIONS

In a class of grand unified models based on SO(10), the mixing angles in the lepton sector are related by symmetry arguments to the measured quark mixing angles. The mixing angles relevant in neutrino oscillations are estimated to be Sin2 2-theta(e-mu) congruent-to 0.02, sin2 2-theta(mu-tau) congruent-to (0.36-1.3) x 10(-2) and sin(2)2-theta(e-tau) congruent-to (0.04-2) x 10(-4). A variety of considerations unrelated to neutrino oscillations enable us to estimate the neutrino masses as well. The heaviest (essentially "tau") neutrino lies in the range 0.5-8 eV, the "muon" neutrino is close to 10(-3) eV, while the "electron" neutrino turns out to be substantially lighter. These predictions can be confronted with recent, ongoing, and proposed neutrino oscillation experiments. As a by-product, one obtains a new understanding of the well-known asymptotic relation m-mu congruent-to 3m(s).