The asymptotic behaviour of the $\pi^0$ $\gamma^\ast$ $\gamma^\ast$ vertex

Abstract

The Bjorken-Johnson-Low theorem applied to the $\gamma^\ast \to \gamma^\ast \pi^0$ process provides us with a rather remarkable asymptotic behaviour for the $\pi^0 \gamma^\ast \gamma^\ast$ vertex. We compare our result with previous QCD- inspired estimates and argue that the predicted behaviour is quite consistent with the present data on hadronic $J/\Psi$ decays and ensures the matching of long- and short-distance radiative corrections to $\pi^+ \to e^+ \nu_e$.