Predictive neutrino spectrum in minimal SO(10) grand unification.

We show that minimal SO(10) Grand Unification models where the fermions have Yukawa couplings to only one (complex) 10 and one 126 of Higgs scalars lead to a very predictive neutrino spectrum. This comes about since the standard model doublet contained in the 126 of Higgs (needed for the see–saw mechanism) receives an induced vacuum expectation value at tree–level, which, in addition to correcting the bad asymptotic mass relations md = me andms = mμ, also relates the Majorana neutrino mass matrix to observables in the charged fermion sectors. We find that (i) the νe−νμ mixing angle relevant for the solar neutrinos can be considerably smaller than the Cabibbo angle and lies in the range sinθeμ = 0 − 0.3, (ii) νe − ντ mixing is sinθeτ ≃ 3|Vtd| ≃ 0.05, (iii) the νμ−ντ mixing angle is large, sinθμτ ≃ 3|Vcb| = 0.12−0.16, and (iv) mντ/mνμ ≥ 10 , implying that νμ − ντ oscillations should be accessible to forthcoming experiments. Supported in part by Department of Energy Grant #DE-FG02-91ER406267 Supported by National Science Foundation Grant PHY-9119745