Journal article

Inverse Hierarchy Approach to Fermion Masses

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) is similar to m(d), m(c) > m(s), m(t) >> m(b). We construct 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)/m(d) > 0.5 and the Cabibbo angle is forced to be is similar to square-root 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 differences between u-, d- and e-type fermions are simply parametrized by three complex coefficients epsilon(u), epsilon(d) and epsilon(e). Additional consistent predictions are obtained: m(s) = 100-150 MeV and m(u)/m(d) < 0.75.

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