Kinematical twist-3 effects in deeply virtual Compton scattering as a quark spin rotation

Abstract

We point out that the kinematical twist-3 contributions to the deeply virtual Compton scattering amplitude, required to restore electromagnetic gauge invariance of the twist-2 amplitude up to O(t/q(2)), can be understood as a spin rotation applied to the twist-2 quark density matrix in the target. This allows for a compact representation of the twist-3 effects, as well as for a simple physical interpretation.