Gauge link structure in quark–quark correlators in hard processes

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.

Origin of model relations among transverse-momentum dependent parton distributions

“…where k þ ¼ xP þ , c is the quark field operator with a, b indices in the Dirac space, and U is the Wilson line which ensures color gauge invariance [37]. The target state is characterized by its four-momentum P and covariant spin four-vector S satisfying P 2 ¼ M 2 , S 2 ¼ À1, and P Á S ¼ 0.…”

Azimuthal and single spin asymmetries in hard scattering processes

“…In Refs. [153,154] the paths that can appear in general scattering processes have been analyzed (some technical aspects are presented in Ref. [155]).…”

Gluonic pole cross sections and single spin asymmetries in hadron-hadron scattering

“…They are related by time-reversal and, correspondingly, the T -odd distribution functions appear with opposite sign. When going beyond these processes one may encounter more complicated gauge-link structures [13,14,15]. Consequently, the simple sign relation between T -odd effects in SIDIS and DY generalizes to color-dependent factors, called gluonic pole factors.…”