Fermion mass hierarchy and non-hierarchical mass ratios in SU(5) x U(1)_F

Understand

We consider a SU(5) x U(1)_F GUT-flavor model in which the number of effects that determine the charged fermions Yukawa matrices is much larger than the number of observables, resulting in a hierarchical fermion spectrum with no particular regularities.

• The GUT-flavor symmetry is broken by flavons in the adjoint of SU(5), realizing a variant of the Froggatt-Nielsen mechanism that gives rise to a large number of effective operators.
• By assuming a common mass for the heavy fields and universality of the fundamental Yukawa couplings, we reduce the number of free parameters to one.
• The observed fermion mass spectrum is reproduced thanks to selection rules that discriminate among various contributions.