New physics in the ZZh vertex: one-loop contributions from a radiative seesaw model

A bstract Precision Higgs physics offers a sensitive window into physics beyond the Standard Model. In parallel, neutrino-oscillation experiments have established the existence of nonzero neutrino masses, thus implying the presence of new physics. Motivated by these facts, we investigate the one-loop contributions of light and heavy Majorana neutrinos to the ZZh vertex within a variant of the type-I seesaw mechanism in which light-neutrino masses vanish at tree level and are then generated radiatively. We analyze the CP -conserving and CP -violating anomalous couplings which characterize the ZZh vertex and study their phenomenological implications in two relevant kinematic scenarios at future lepton colliders: Higgsstrahlung production and Higgs production via neutral-current vector-boson fusion. We find that CP -conserving effects can reach magnitudes of order 10 −3 , potentially within projected future experimental sensitivities, whereas CP -violating contributions are strongly suppressed, lying well beyond such projections.