On the two-loop BSM corrections to $h\longrightarrow \gamma\gamma$ in a triplet extension of the SM

TL;DR

This paper calculates two-loop beyond Standard Model corrections to the Higgs to diphoton decay in a triplet-extended SM, providing explicit formulas and discussing their importance for precise decay width predictions.

Contribution

It introduces explicit formulas for two-loop BSM corrections to Higgs decay in a triplet extension, focusing on scalar quartic couplings and their numerical impact.

Findings

Two-loop BSM contributions can significantly affect the Higgs to diphoton decay width.

Explicit formulas derived using a low-energy theorem facilitate precise calculations.

Numerical analysis shows the importance of these corrections when scalar quartic couplings are large.

Abstract

We compute the two-loop BSM contributions to the $h\longrightarrow \gamma\gamma$ decay width in the SM extended with a real triplet of $SU(2)$. We consider scenarios in which the neutral components of doublet and triplet do not mix, so that the lighter neutral scalar $h$ has (at least approximately) SM-like couplings to fermions and gauge bosons. We focus on the two-loop corrections controlled by the quartic scalar couplings, and obtain explicit and compact formulas for the $h \gamma \gamma$ amplitude by means of a low-energy theorem that connects it to the derivative of the photon self-energy w.r.t. the Higgs field. We briefly discuss the numerical impact of the newly-computed contributions, showing that they may be required for a precise determination of $\Gamma[h\rightarrow \gamma \gamma]$ in scenarios where the quartic scalar couplings are large.