Two-photon decays and transition form factors of π0, η, and η′ in large-Nc chiral perturbation theory

We present a calculation of P→γ(*)γ(*) processes, where P=π0,η,η′, at the one-loop level up to and including next-to-next-to-leading order (NNLO) in large-Nc chiral perturbation theory. The results are numerically evaluated successively at LO, NLO, and NNLO. The appearing low-energy constants are determined through fits to the available experimental data. We investigate the decay widths to real photons, the single-virtual transition form factors, and the widths of P→γl+l−, where l=e, μ. Furthermore, we provide results for the slopes and curvatures of the transition form factors.