Twist-three analysis of photon electroproduction off the pion

We study twist-three effects in spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering on a spin-zero target. Contributions which 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 contributions. They may get corrected at the twist-four level, however. In the Wandzura-Wilczek approximation these new terms in the Fourier expansion with respect to the azimuthal angle 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 section, the validity of factorization at the twist-three level, and the relation of generalized parton distributions to spectral functions.