Inverse hierarchy approach to fermion masses

Abstract

The first fermion family might play a special role in understanding the physics of flavour. This possibility is suggested by the observation that the up-down splitting within quark families increases with the family number: m u d , m c > m s , m t ⪢ m b . We constrruct a model that realizes this feature of the spectrum in a natural way. The inter-family hierarchy is first generated by radiative phenomena in a sector of heavy isosinglet fermions and then transferred to quarks by means of a universal seesaw. A crucial role is played by left-right parity and up-down isotopic symmetry. No family symmetry is introduced. The model implies m u/ md > 0.5 and the Cabibbo angle is forced to be ∼√ m d / m s . The top quark is naturally in the 100 GeV range, but not too heavy: m t <150 GeV. Inspired by the mass matrices obtained in the model for quarks, we suggest an ansatz also including charged leptons. The difference between u-, d- and e-type fermions are simply parametrized by three complex coefficients ϵ u , ϵ d and ϵ e . Additional comnsistent predictions are obtained: m s = 100–150 MeV and m u / m d <0.75.