Constraining gluon poles

TL;DR

This paper revises QED gauge invariance in Drell-Yan processes with transversely polarized hadrons, showing that gluon poles are absent in gauge-invariant correlators, which impacts the theoretical understanding of these processes.

Contribution

It demonstrates that QED gauge invariance eliminates gluon poles in certain correlators, introducing a non-standard diagram and clarifying the gauge dependence in Drell-Yan processes.

Findings

Gluon poles are absent in gauge-invariant correlators.

A non-standard diagram is necessary for gauge invariance.

Gluon pole terms disappear from the hadron tensor.

Abstract

In this letter, we revise the QED gauge invariance for the hadron tensor of Drell-Yan type processes with the transversely polarized hadron. We perform our analysis within the Feynman gauge for gluons and make a comparison with the results obtained within the light-cone gauge. We demonstrate that QED gauge invariance leads, first, to the need of a non-standard diagram and, second, to the absence of gluon poles in the correlators $\langle\bar\psi\gamma_\perp A^+\psi\rangle$ related traditionally to $dT(x,x)/dx$. As a result, these terms disappear from the final QED gauge invariant hadron tensor. We also verify the absence of such poles by analysing the corresponding light-cone Dirac algebra.