Generalized Universality for TMD Distribution Functions

TL;DR

This paper introduces a framework for defining universal transverse momentum dependent (TMD) distribution functions with definite rank, accounting for process-dependent Wilson lines and gluonic pole factors, enhancing understanding of azimuthal asymmetries in high-energy physics.

Contribution

It proposes a set of universal TMDs of definite rank that incorporate process dependence via gluonic pole factors, extending the universality concept in TMD physics.

Findings

Defined universal TMDs with process-dependent factors.

Identified three pretzelocity functions for spin 1/2 targets.

Clarified the role of Wilson lines in TMD universality.

Abstract

Azimuthal asymmetries in high-energy processes, most pronounced showing up in combination with single or double (transverse) spin asymmetries, can be understood with the help of transverse momentum dependent (TMD) parton distribution and fragmentation functions. These appear in correlators containing expectation values of quark and gluon operators. TMDs allow access to new operators as compared to collinear (transverse momentum integrated) correlators. These operators include nontrivial process dependent Wilson lines breaking universality for TMDs. Making an angular decomposition in the azimuthal angle, we define a set of universal TMDs of definite rank, which appear with process dependent gluonic pole factors in a way similar to the sign of T-odd parton distribution functions in deep inelastic scattering or the Drell-Yan process. In particular, we show that for a spin 1/2 quark target there are three pretzelocity functions.