Spin Filter in DVCS amplitudes

In deeply virtual Compton scattering (DVCS) it is found that in some kinematics angular momentum is not conserved if the amplitudes are calculated in terms of widely used reduced operators. Consequently, those kinematics will lead to the wrong analysis of experimental data in terms of generalized parton distributions. Contrary to common lore, the contribution of the longitudinally polarized virtual photon should not be neglected in the analysis of DVCS amplitudes.