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 m d = m e and m s = m µ , also relates the Majorana neutrino mass matrix to observables in the charged fermion sectors. We find that (i) the ν e − ν µ mixing angle relevant for the solar neutrinos can be considerably smaller than the Cabibbo angle and lies in the range sinθ eµ = 0 − 0.3, (ii) ν e − ν τ mixing is sinθ eτ ≃ 3|V td | ≃ 0.05, (iii) the ν µ −ν τ mixing angle is large, sinθ µτ ≃ 3|V cb | = 0.12−0.16, and (iv) m ντ /m νµ ≥ 10 3 , implying that ν µ − ν τ oscillations should be accessible to forthcoming experiments.

Centre d'études et d'expertise sur les risques, l'environnement, la mobilité et l'aménagement

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We review the present state and future outlook of our understanding of neutrino masses and mixings. We discuss what we think are the most important perspectives on the plausible and natural scenarios for neutrinos and attempt to throw light onto the flavor problem of quarks and leptons. This review focuses on the seesaw mechanism, which fits into a big picture of particle physics such as supersymmetry and grand unification providing a unified approach to the flavor problem of quarks and leptons. We argue that in combination with family symmetries, this may be at the heart of a unified understanding of the flavor puzzle. We also discuss other new physics ideas such as neutrinos in models with extra dimensions and possible theoretical implications of sterile neutrinos. We outline some tests for the various schemes.

No abstract