Large mixing angles in a SU(2)_L gauge theory of weak interactions as a resonant effect of 1-loop transitions between quasi-degenerate fermions

We show that 1-loop transitions between two quasi-degenerate fermions can induce a potentially large renormalization of their mixing angle, and a large renormalized Cabibbo (or PMNS) angle when the second fermion pair in the same two generations is far from degeneracy. At the resonance, the Cabibbo angle gets maximal and simply connected to masses without invoking any new physics beyond the standard model. This solution appears as the only one perturbatively stable (mixing angles are then renormalized with respect to their classical values by small amounts).