Speaker
Description
Hard exclusive processes play a prominent role in exploring the strong interaction dynamics of hadronic reactions in the framework of QCD. In this context, the pion-photon transition form factor $\gamma \gamma^\ast \to \pi^0$ at large momentum transfer serves as one of the simplest exclusive processes for testing the theoretical predictions based upon perturbative QCD factorization.
Whereas the one-loop perturbative and certain power-suppressed contributions are already known and turn out to be important in view of precise experimental measurements and the scaling violation implied by the BaBar data, the two-loop correction at leading power remained unknown until recently.
Here we report on the two-loop calculation of the pion-photon transition form factor from the process $\gamma \gamma^\ast \to \pi^0$ at leading power. Besides discussing the applied multi-loop techniques, we put emphasis on the infrared subtraction and the role of evanescent operators, and present some numerical results.
