Non-universality of transverse momentum dependent parton distribution functions

TL;DR

This paper investigates how process-dependent interactions in hadronic scattering cause non-universality in transverse momentum dependent parton distribution functions, impacting factorization approaches in high-energy physics.

Contribution

It systematically separates universal and non-universal parts of TMD correlators, highlighting their implications for factorization in hadron-hadron scattering processes.

Findings

Identifies process dependence in TMD PDFs due to gluon interactions.

Separates universal T-even and T-odd parts from process-dependent components.

Shows the relevance of gluonic pole cross sections in factorization.

Abstract

In the field theoretical description of hadronic scattering processes, single transverse-spin asymmetries arise due to gluon initial and final state interactions. These interactions lead to process dependent Wilson lines in the operator definitions of transverse momentum dependent parton distribution functions. In particular for hadron-hadron scattering processes with hadronic final states this has important ramifications for possible factorization formulas in terms of (non)universal TMD parton distribution functions. In this paper we will systematically separate the universality-breaking parts of the TMD parton correlators from the universal T-even and T-odd parts. This might play an important role in future factorization studies for these processes. We also show that such factorization theorems will (amongst others) involve the gluonic pole cross sections, which have previously been shown to describe the hard partonic scattering in weighted spin asymmetries.