On the Wandzura-Wilczek approximation for the twist-3 DVCS amplitude

We present a derivation of Wandzura-Wilczek (WW) like relations for skewed parton distributions. It is demonstrated for photon-pion scattering that for transverse photon polarization the skewed twist-3 parton distributions contributing to the DVCS amplitude have discontinuities at the points $x=\pm\xi$ in the WW approximation. Unless these discontinuities are cancelled by the neglected genuine higher twist pieces they lead to a violation of factorisation for the twist-3 DVCS amplitude with transverse polarization of the virtual photon. For the scattering of longitudinally polarized photon the twist-3 amplitude is free of such divergencies.