Grand Unification of Fermion Masses

Abstract

After a brief review of the flavour problem we present a new predictive framework based on SUSY $SO(10)$ theory, where the first family plays a role of the mass unification point. The inter-family hierarchy is first generated in a sector of superheavy fermions and then transfered in an inverse way to ordinary quarks and leptons by means of the universal seesaw mechanism. The obtained mass matrices are simply parametrized by two small coefficients which can be given by the ratio of the GUT and superstring compactification scales. The model allows a natural (without fine tuning) doublet-triplet splitting. It has a strong predictive power, though no special texture is utilized in contrast to the known predictive frameworks. Namely, the model implies that $m_b=4-5$ GeV, $m_s=100-150$ MeV, $m_u/m_d=0.5-0.7$ and $\tan\beta<1.1$. The Top quark is naturally in the 100 GeV range, but not too heavy: $m_t<150$ GeV. All CKM mixing angles are in correct range. The Higgsino mediated $d=5$ operators for the proton decay are naturally suppressed. {On the basis of talks given at the XVI International Warsaw Meeting on Elementary Particle Physics "New Physics with New Experiments", Kazimierz, Poland, 24-28 May 1993, and at the II Gran Sasso Summer Institute "From Particle Physics to Cosmology", Gran Sasso National Laboratory, Italy, 6-17 September 1993.}