POLARIZED DRELL-YAN AND DIRECT PHOTON PRODUCTION PROCESSES: CONTOUR GAUGE, TWIST THREE AND GLUON POLES

We discuss the different aspects of the contour gauge condition used intensively in the past in the studies of the QFT infra-red (IR) sector. We apply this conception to the study of dominant contributions to the polarized Drell-Yan (DY) and direct photon production (DPP) hadron tensors. Making use of the contour gauge, which is a nonlocal generalization o usual axial gauge, we prove the existence of new contributions to the hadron tensors which ultimately restore the gauge invariance of hadron tensors and play an important role in the QCD factorization theorem.The practical applications of new contributions are discussed.

All interested persons are invited.
M. Kowal, W. Piechocki, L. Roszkowski, J. Skalski, L. Szymanowski