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

TL;DR

This paper studies how one-loop effects from Majorana neutrinos in a radiative seesaw model can modify the $ZZh$ vertex, with potential observable consequences at future lepton colliders.

Contribution

It introduces a novel analysis of radiative neutrino mass effects on the $ZZh$ vertex within a specific seesaw model, including both $CP$-conserving and violating couplings.

Findings

$CP$-conserving effects can reach order $10^{-3}$, within future collider sensitivity.

$CP$-violating effects are highly suppressed, beyond projected experimental reach.

The model's implications are analyzed in Higgsstrahlung and vector-boson fusion scenarios.

Abstract

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.