0 Twist - three analysis of photon electroproduction off pion

Twist-three analysis of photon electroproduction off pion. Abstract We study twist-three effects in spin, charge, and azimuthal asymmetries in deeply virtual Compton scattering off a spin-zero target. Power suppressed contributions generate a new azimuthal angle dependence in the cross section, not present in the leading twist approximation. On the other hand the structures induced by the latter do not get corrected by twist-three effects and expected to be affected at most at twist-four level. It is shown that in the Wandzura-Wilczek approximation all terms in the Fourier expansion with respect to the azimuthal angle are entirely determined by the twist-two skewed parton distribution. We also discuss more general issues like a general form of angular dependence in the differential cross section, validity of factorization at twist-three level, and relation of skewed parton distributions to spectral functions.