Eur. Phys. J. C 20, 271-281
Spin-dependent structure functions of real and virtual photonsM. Glück, E. Reya and C. Sieg
Universität Dortmund, Institut für Physik, 44221 Dortmund, Germany
(Received: 16 March 2001 / Published online: 18 May 2001 -© Springer-Verlag / Società Italiana di Fisica 2001)
The implications of the positivity constraint, , on the presently unknown spin-dependent structure function of real and virtual photons are studied at scales where longitudinally polarized photons dominate physically relevant cross sections. In particular it is shown how to implement the physical constraints of positivity and continuity at P2=0 in NLO calculations which afford a nontrivial choice of suitable (DIS) factorization schemes related to and and appropriate boundary conditions for the polarized parton distributions of real and virtual photons. The predictions of two extreme `maximal' and `minimal' saturation scenarios are presented and compared with results obtained within the framework of a simple quark `box' calculation expected to yield reasonable estimates in the not too small regions of x and P2.
© Società Italiana di Fisica, Springer-Verlag 2001