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arXiv · hep-ph/0408249

Universality of soft and collinear factors in hard-scattering factorization

John C. Collins·Andreas Metz
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Abstract

Universality in QCD factorization of parton densities, fragmentation functions, and soft factors is endangered by the process dependence of the directions of Wilson lines in their definitions. We find a choice of directions that is consistent with factorization and that gives universality between e^+e^- annihilation, semi-inclusive deep-inelastic scattering, and the Drell-Yan process. Universality is only modified by a time-reversal transformation of the soft function and parton densities between Drell-Yan and the other processes, whose only effect is the known reversal of sign for T-odd parton densities like the Sivers function. The modifications of the definitions needed to remove rapidity divergences with light-like Wilson lines do not affect the results.

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John C. Collins, Andreas Metz. 2004-12-10. Universality of soft and collinear factors in hard-scattering factorization. https://doi.org/10.1103/physrevlett.93.252001

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