$H\to \gamma \gamma$ to all orders in ${\alpha }_s$ in the large-${\beta }_0$ limit of QCD

In this note, we present the result for the QCD corrections to the decay of the Higgs boson into two photons in the large-${\beta }_0$ limit of QCD, providing the first two terms in the heavy-top expansion. From our results, one can easily read off the exact leading-$n_f$ QCD contributions in analytic form to all orders in the strong coupling, ${\alpha }_s$, where $n_f$ is the number of massless quarks, and identify the leading renormalon singularities. We give explicit results for the leading-$n_f$ coefficients at 6 and 7 loops and use the large-${\beta }_0$ result to speculate about the size of yet unknown (but small) higher-order contributions to the QCD series.