ar X iv : h ep - p h / 02 02 14 2 v 2 1 8 A pr 2 00 2 Polarized Virtual Photon Structure Function g γ 2 and Twist - 3 Effects in QCD

We investigate the twist-3 effects in the polarized virtual photon structure. The structure functions g 1 and g γ 2 of polarized photon could be experimentally studied in the future polarized ep or ee colliders. The leading contributions to g 1 are the twist-2 effects, while another structure function g 2 , which only exists for the virtual photon target, receives not only the twist-2 but also twist-3 contributions. We first show that the twist-3 effects actually exist in the box-diagram contributions and we extract the twist-3 part, which can also be reproduced by the pure QED operator product expansion. We then calculate the non-trivial lowest moment (n = 3) of the twist-3 contribution to g 2 in QCD. For large Nc (the number of colors), the QCD analysis of the twist-3 effects in the flavor nonsinglet part of g 2 becomes tractable and we can obtain its moments in a compact form for all n. YNU-HEPTh-02-101 KUCP-201, revised April 2002 e-mail address: [email protected] e-mail address: [email protected] e-mail address: [email protected]