Polarized Photon Structure: g γ 1 and g γ

In the last ten years, the spin-dependent structure functions g1 and g2 of the nucleon have been intensively studied in the polarized deep-inelastic scattering of polarized lepton on polarized nucleon targets. Based on the next-to-leading order (NLO) QCD analysis of the experimental data, the polarized parton distributions inside the nucleon have been extracted. The gluon polarization ∆G is now one of the central issues in spin physics. On the other hand, there has been growing interest in the polarized photon structure functions. Especially the first moment of a photon structure function g 1 has attracted much attention in the literature [1, 2, 3, 4, 5] in connection with the axial anomaly which is also relevant in the nucleon spin structure function g p(n) 1 . The polarized structure function g γ 1 could be experimentally studied in the polarized version of ep collider HERA [6, 7], or more directly measured by the polarized ee collision in the future linear collider. And the next-to-leading order QCD analysis of g 1 has been performed in the literature [8, 9, 10, 11]. Now there exists another structure function g 2 for the virtual photon target, where the twist-3 effect is also relevant in addition to the usual twist-2 effect. In this talk, we first briefly summarize our results for the g 1 for the virtual photon target, and then investigate the twist-3 effects in g 2 .