On the two-loop BSM corrections to in a triplet extension of the SM

Giuseppe Degrassi; Pietro Slavich

doi:10.1140/epjc/s10052-025-13758-1

2024 Impact factor 4.8

Particles and Fields

Open Access

Eur. Phys. J. C (2025) 85: 49
https://doi.org/10.1140/epjc/s10052-025-13758-1

Regular Article - Theoretical Physics

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

Giuseppe Degrassi¹ and Pietro Slavich²^a

¹ Dipartimento di Matematica e Fisica, Università di Roma Tre, INFN, Sezione di Roma Tre, 00146, Rome, Italy
² Sorbonne Université, CNRS, Laboratoire de Physique Théorique et Hautes Energies, LPTHE, 75005, Paris, France

^a slavich@lpthe.jussieu.fr

Received: 5 August 2024
Accepted: 30 December 2024
Published online: 22 January 2025

Abstract

We compute the two-loop BSM contributions to the $h ⟶ γ γ$ $h\longrightarrow \gamma \gamma$ 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 $h γ γ$ $h \gamma \gamma$ 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 $Γ [h \to γ γ]$ $\Gamma [h\rightarrow \gamma \gamma ]$ in scenarios where the quartic scalar couplings are large.

© The Author(s) 2025

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