Perturbative unitarity constraints on generic Yukawa interactions

Abstract We study perturbative unitarity constraints on generic Yukawa interactions where the involved fields have arbitrary quantum numbers under an ∏iSU(Ni) ⊗ U(1) group. We derive compact expressions for the bounds on the Yukawa couplings for the cases where the fields transform under the trivial, fundamental or adjoint representation of the various SU(N) factors. We apply our results to specific models formulated to explain the anomalous measurements of (g − 2)μ and of the charged- and neutral-current decays of the B mesons. We show that, while these models can generally still explain the observed experimental values, the required Yukawa couplings are pushed at the edge of the perturbative regime.