Revisiting the Higgs Boson Decay into a Photon and a Neutrino Pair

We present new calculations of the leading-order one-loop amplitude and the decay rate for H→ ν̄ν γ within the standard model, employing reduction to a set of basic Passarino-Veltman functions resulting in a more concise expressions compared to prior works. Our result for the total decay rate is Γ(H→ ν̄ν γ)=1.33\,keV, in close agreement with the narrow width approximation (NWA) for the intermediate Z boson. We also provide a comparison with previous results available in the literature. We evaluate the differential decay rate and find that the non-resonant contributions from box diagrams beyond the NWA notably affect the off-shell kinematic region associated with high-energy photons, suggesting potential implications for dark sector mediators, particularly in future lepton collider experiments.