title: Universality of soft and collinear factors in hard-scattering factorization.
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 such as the Sivers function. The modifications of the definitions needed to remove rapidity divergences with lightlike Wilson lines do not affect the results.
authors.affiliation: Pennsylvania State University, 104 Davey Lab, University Park, Pennsylvania 16802, USA.
authors.forename: John C
authors.initials: JC
authors.lastname: Collins
authors.forename: Andreas
authors.initials: A
authors.lastname: Metz