Quark Orbital Angular Momentum in the Wandzura-Wilczek Approximation

Abstract

We show that quark orbital angular momentum is directly related to off-forward correlation functions which include intrinsic transverse momentum corresponding to a derivative with respect to the transverse coordinates. Its possible contribution to scattering processes is therefore of higher twist and vanishes in the forward limit. The relation of OAM to other twist 2 and 3 distributions known in the literature is derived and formalized by an unintegrated sum rule.

Comments: 10 pages; Several points clarified, 3 references added, to be published in PLB