On the large-Q^2 behavior of the pion transition form factor

We study the transition of non-perturbative to perturbative QCD in situations with possible violations of scaling limits. To this end we consider the singly- and doubly-virtual pion transition form factor pi^0-->gamma gamma at all momentum scales of symmetric and asymmetric photon momenta. For the doubly virtual form factor we find good agreement with perturbative asymptotic scaling laws. For the singly-virtual form factor our results agree with the Belle data. At asymptotically large photon momenta we identify a novel mechanism that introduces sizeable modifications to the Efremov-Radyushkin-Brodsky-Lepage limit.