Twist-three analysis of photon electroproduction off the pion - art. no. 116002

We study twist-three effects in spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering on a spin-zero target. Contributions whic h are power suppressed in 1/Q generate a new azimuthal angle dependence of the cross section that is not present in the leading twist results. On the other hand, the leading twist terms are not modified by the twist-three con tributions. They may get corrected at the twist-four level, however. In the Wandzura-Wilczek approximation these new terms in the Fourier expansion wi th respect to the azimuthal an le are entirely determined by the twist-two generalized parton distributions. We also discuss more general issues such as the general form of the angular dependence of the differential cross sec tion, the validity of factorization at the twist-three level, and the relat ion of generalized parton distributions to spectral functions.