Abstract
Distribution functions in hard processes can be described by quark–quark correlators, nonlocal matrix elements of quark fields. Color gauge invariance requires inclusion of appropriate gauge links in these correlators. For transverse momentum dependent distribution functions, in particular important for describing T-odd effects in hard processes, we find that new link structures containing loops can appear in Abelian and non-Abelian theories. In transverse moments, e.g., measured in azimuthal asymmetries, these loops may enhance the contribution of gluonic poles. Some explicit results for the link structure are given in high-energy leptoproduction and hadron–hadron scattering.
Highlights
In this Letter we discuss the issue of color gauge invariance in bilocal operator matrix elements off the lightcone [1]
Such matrix elements are relevant in hard processes in which transverse momenta of partons play a role such as semi-inclusive deep inelastic scattering (SIDIS) or the Drell–Yan process (DY)
As argued in [6], the combination of these two mechanisms spoils the simple sign relation between unintegrated fragmentation functions appearing in SIDIS and electron–positron annihilation found in Ref. [20], which uses the model of Ref. [21]
Summary
In this Letter we discuss the issue of color gauge invariance in bilocal operator matrix elements off the lightcone [1]. Such matrix elements are relevant in hard processes in which transverse momenta of partons play a role such as semi-inclusive deep inelastic scattering (SIDIS) or the Drell–Yan process (DY). In these two cases the quark correlation functions that appear at leading order in an expansion in the inverse hard scale turn out to have a different gauge link structure. Bomhof et al / Physics Letters B 596 (2004) 277–286 by the explicit presence of gluons will be discussed at the end, but the full treatment will be done as part of yet to come applications to hard QCD processes
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