Asymmetries associated with higher twists: gauge invariance, gluonic poles and twist three

TL;DR

This paper investigates the gauge invariance of the hadron tensor in the Drell-Yan process with transverse polarization, revealing how gluonic poles and contour gauge choices influence single spin asymmetries and their enhancement.

Contribution

It establishes a connection between gluonic pole prescriptions, causality, and gauge invariance, introducing additional contributions that affect asymmetry calculations.

Findings

Gluonic pole prescriptions relate to causality in exclusive processes.

Extra contributions enhance the single spin asymmetry by a factor of two.

Contour gauge plays a crucial role in gauge invariance analysis.

Abstract

We explore the electromagnetic gauge invariance of the hadron tensor of the Drell-Yan process with one transversely polarized hadron. Due to the special role of the contour gauge for gluon fields, the prescription for the gluonic pole in the twist 3 correlator can be related to the causality prescriptions for exclusive hard processes. Because of this, we find the extra contributions, which naively do not have an imaginary phase. The single spin asymmetry for the Drell-Yan process is accordingly enhanced by the factor of two.