Wandzura–Wilczek approximation from generalized rotational invariance

We present the alternative way of derivation of the Wandzura–Wilczek relations between the kinematical twist-3 and twist-2 functions, parameterizing hadronic matrix element in two-photon processes γ★π→γπ and γ★γ→ππ. The new equations, providing the independence of the physical cross-sections on the choice of the light-cone direction, are suggested and explored. The amplitude of γ★γ→ππ up to genuine twist-3 accuracy is found.