Twist-3 effects in deeply virtual Compton scattering made simple

Abstract

We show that electromagnetic gauge invariance requires a 'spin rotation' of the quarks in the usual twist-2 contribution to the amplitude for deeply virtual Compton scattering. This rotation is equivalent to the inclusion of certain kinematical twist-3 (Wandzura-Wilczek type) terms, which have been derived previously using other methods. The new representation of the twist-3 terms is very compact and allows for a simple physical interpretation.Comment: 4 pages, 3 figures, uses ws-p8-50x6-00.cls . Proceedings of the Baryons 2002 Conference, Jefferson Lab, Newport News, VA, March 3-8, 200