Abstract

We show that the first moment of the spin-dependent structure function g1 ?(x,Q2) of a real photon vanishes independent of the momentum transfer Q2 it is probed with. This result is non-perturbative: it holds to all orders in perturbation theory in abelian and non-abelian gauge theory and at every twist. © 1998 Elsevier Science B.V. All rights reserved.