On the two-loop BSM corrections to $h\longrightarrow \gamma \gamma $ in the aligned THDM

We compute the two-loop BSM contributions to the $$h\longrightarrow \gamma \gamma $$h ⟶ γ γ decay width in the aligned THDM. We adopt the simplifying assumptions of vanishing EW gauge couplings and vanishing mass of the SM-like Higgs boson, which allow us to exploit a low-energy theorem connecting the $$h\gamma \gamma $$h γ γ amplitude 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 $$\Gamma [h\rightarrow \gamma \gamma ]$$Γ [ h → γ γ ] in scenarios where the quartic Higgs couplings are large.