A model independent analysis of gluonic pole matrix elements and universality of TMD fragmentation functions

TL;DR

This paper demonstrates that gluonic pole matrix elements vanish for TMD fragmentation functions due to the analytic structure of QCD amplitudes, impacting the understanding of their universality in high-energy scattering.

Contribution

It provides a model-independent proof that gluonic pole matrix elements are zero for TMD fragmentation functions, clarifying their role in single spin asymmetries.

Findings

Gluonic pole matrix elements vanish for fragmentation functions.

Implication for the universality of TMD fragmentation functions.

Enhances understanding of T-odd effects in QCD processes.

Abstract

Gluonic pole matrix elements explain the appearance of single spin asymmetries (SSA) in high-energy scattering processes. They involve a combination of operators which are odd under time reversal (T-odd). Such matrix elements appear in principle both for parton distribution functions and parton fragmentation functions. We show that for parton fragmentation functions these gluonic pole matrix elements vanish as a consequence of the analytic structure of scattering amplitudes in Quantum Chromodynamics. This result is important in the study of the universality of transverse momentum dependent (TMD) fragmentation functions.