New rare meson decay constraints on a light vector in U(1)B−L, U(1)R and the dark photon

A bstract We evaluate constraints from flavor changing rare meson decays to a light vector boson X , followed by the decay of the on-shell X into the SM fermions. The flavor changing meson decay emitting the light X is induced by loop processes where the up-type quarks, the W boson, or charged scalar bosons are running inside loops. We calculate all one-loop diagrams with neglecting all masses of light quarks except for the top quark in a general anomaly free extra U(1) model. Our theoretical evaluation of the branching ratio of charged B meson decay and charged kaon decay is compared to experimental results, and we derive new constraints for dark photon, U(1) B−L and U(1) R models.