Speaker
Description
This talk presents two studies related to the one-loop CSS evolution of TMD distributions within the background field method, in the target light-cone gauge (making the partonic picture for the hadron target manifest).
The first study concerns the potential effect of the residual gauge freedom in the light-cone gauge and of the prescriptions proposed to address it. We consider on the one hand the Mandelstam-Leibbrandt (ML) prescription, defined in terms of two light-cone vectors, and on the other hand an infinite family of prescriptions defined with a single light-cone vector, including principal value, retarded and advanced prescriptions. In both cases, the standard result for CSS evolution for quark TMDs is recovered, but from radically different contributions from individual diagrams, and with further potential issues in the second case.
TMD factorization is proven for processes in which two of the incoming or outgoing particles in the hard factor are colored partons. In that case, the factorization formula involves two TMDs, each with a staple-shaped gauge link, pointing in either the past or future direction. In processes with more than two colored partons, not only more than two TMDs should be introduced, but some of them can involve more and more exotic gauge links. In particular one can encounter the so-called dipole gluon TMDs, which includes both a past and a future staple in its gauge link, and which often appears in the small x QCD literature. In the second study, we calculate the one-loop correction to the dipole gluon TMDs within the background field method in the target light-cone gauge, and compare it to the case of gluon TMDs with standard staple gauge link (a.k.a. Weizsäcker-Williams gluon TMDs), in order to clarify to what extent the standard CSS evolution could stay valid for the dipole gluon TMDs.