Next-to-leading-order electroweak correction to $H\to Z^0\gamma$

TL;DR

This paper calculates the NLO electroweak correction to the rare Higgs decay into Z gamma, finding it significantly impacts the predicted decay width and highlights a discrepancy with experimental measurements.

Contribution

It provides the first detailed analysis of NLO electroweak effects on $H o Z^0\gamma$ decay within the Standard Model, revealing a larger correction than previously estimated.

Findings

NLO electroweak correction can reach 7% of LO prediction.

Predicted branching ratio increases from 1.40-1.71×10^{-3} to 1.55±0.06×10^{-3}.

Significant discrepancy remains between SM prediction and experimental data.

Abstract

Inspired by the recent observation of the Higgs boson radiative decay into $Z^0$ by {\tt ATLAS} and {\tt CMS} Collaborations, we investigate the next-to-leading-order (NLO) electroweak correction to this rare decay process in Standard Model (SM). Implementing the on-shell renormalization scheme, we find that the magnitude of the NLO electroweak correction may reach $7\%$ of the leading order (LO) prediction, much more significant than that of the NLO QCD correction, which is merely about $0.3\%$. After incorporating the ${\cal O}(\alpha)$ correction, the predicted partial width from various $\alpha$ schemes tend to converge to each other. Including both NLO electroweak and QCD corrections, the SM prediction for the branching fraction shifts from the LO value of $(1.40-1.71)\times 10^{-3}$ to $(1.55\pm 0.06)\times 10^{-3}$, considerably lower than the measured value ${\cal B}_{\rm exp}[H\to Z^0\gamma]=(3.4\pm 1.1)\times 10^{-3}$. Resolving this alarming discrepancy clearly calls for further theoretical investigations, and, more importantly, experimental efforts from {\tt HL-LHC} and the prospective Higgs factories such as {\tt CEPC} and {\tt FCC-ee}.