Higgs decays to two leptons and a photon beyond leading order in the SMEFT

TL;DR

This paper calculates the Higgs decay into two leptons and a photon within the SMEFT framework, including full one-loop Standard Model effects and dimension-eight operators, to improve understanding of potential new physics signatures.

Contribution

It provides the first full one-loop Standard Model and dimension-eight SMEFT calculation for this decay channel, enhancing the ability to distinguish UV completions and operator classes.

Findings

The decay channel can differentiate strongly and weakly interacting UV completions.

It allows identification of specific SMEFT operator classes, including contact operators.

The calculation improves the precision of Higgs decay predictions in SMEFT.

Abstract

We present the three-body decay of the Higgs boson into two leptons and a photon to dimension-eight in the Standard Model Effective Field Theory (SMEFT). In order to obtain this result we interfere the full one-loop Standard Model result with the tree-level result in the SMEFT. This is the first calculation of the partial width of the Higgs boson into two leptons and a photon in the SMEFT to incorporate the full one-loop dependence for the Standard Model as well as the full tree level dimension-eight dependence in the SMEFT. We find that this channel can aid in distinguishing strongly interacting and weakly interacting UV completions of the SMEFT under standard assumptions. We also find that this channel presents the opportunity to distinguish different operator Classes within the SMEFT, potentially including contact $H\bar\ell\ell\gamma$ operators which are first generated only at dimension-eight in the SMEFT.