Perturbative QCD and New Development of Spin Physics

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In the present research project, we have investigated the high-energy spin physics aiming at its new development, based on the framework of the perturbative QCD, utilizing the Operator Product Expansion (OPE) together with the renormalization group as well as the parton picture described by the DGLAP type evolution equation. In the first year, we have studied the spin structure function g_1 of the photon measured by the polarized electron-positron collision and the spin-dependent parton distributions of the quark and gluon inside the polarized virtual photon, to the next-to-leading-log order of QCD. In this respect, we have shows that the parton distributions depend on the factorization scheme as well as the characteristic features of each scheme based on the actual perturbative calculation, in the higher-order of the perturbation theory. On the other hand, in the second and the third (last) years of this research project, we clarified the higher-twist effects, especially that there ap … More pears the twist-3 effect is the g_2 structure function of the polarized virtual photon. We have shows this first by the QED Box diagram calculation and then the OPE analysis for the case of pure QED interaction. We further extruded this result to the case including the QCD interaction, in particular, the exact third moment of g_2 structure function to the leading-log order as well as the large N_c limit of the x dependence of the flavor-nonsinglet part. We also investigated the positivity constraint on the eight structure functions of the virtual photon and intiated the target mass effects of virtual photon target in the framework of O(4) expansion and Nachtmann moments. In the course of the present research, discussions and communications with the people in the related fields were very useful. Especially, we are very much indebted to the communications with the researchers at University of Tokyo, Hiroshima University, Yokohama National University, RIKEN and DESY. We have published our results at JPS meeting and the international workshops at the domestic as well as foreign research Institutes. These results have been published in the journals listed above. Less