Constrained Flavor Breaking

We explore predictive flavor models based on subgroups of the standard-model $SU(3{)}^5$ flavor symmetry. Restricting to products of $SU(3)$, we find that a global $SU(3{)}^3$ flavor symmetry, broken only by two Yukawa spurions, leads to a relation among down-type quark, up-type quark and charged-lepton Yukawa matrices: $Y_d\propto Y_u{Y}_e^{†}$. As a result, the charged-lepton mass ratios are expressed in terms of quark mass ratios and mixing angles. Large leptonic mixing angles appear to be natural and lead to contributions to flavor-changing neutral currents in the charged-lepton sector, which can be tested in future precision experiments.