Power corrections to the process $\gamma {\gamma }^{\ast }\to \pi \pi$ in the Light-Cone Sum Rules approach

Abstract

We applied QCD Light Cone Sum Rules to estimate power corrections to the helicity-conserving amplitude in the process ${\gamma }^{\ast }\gamma \to \pi \pi$. We found that above $Q^2\sim 4$ GeV${}^2$ power corrections are numerically small and the twist-2 part dominates.The amplitude can be reliably calculated in this region using models of $2\pi$ distribution amplitudes as an input. We found that the magnitude of the NLO corrections depends rather strongly on the normalization of the gluonic distribution amplitude.

Comments: 20 pages, 6 figures