Sivers Asymmetry and Generalized Parton Distributions in Impact Parameter Space

TL;DR

This work investigates the Sivers asymmetry in SIDIS by embedding generalized parton distributions in impact parameter space within a scalar diquark model. It shows that a transverse distortion of the parton distribution, governed by the GPD E, combines with final-state interactions to generate a momentum-space Sivers effect, providing a concrete realization of the SSA = GPD E * FSI idea. The analysis links the sign and magnitude of the distortion to the anomalous magnetic moment κ_q and the orbital angular momentum content, offering an intuitive, model-based picture of how transverse spin phenomenology arises from QCD dynamics. These results clarify the mechanism by which transverse position space structure translates into a Sivers asymmetry in momentum space and illuminate the role of orbital angular momentum in generating SSAs.

Abstract

Recently, it has been pointed out that there exists a connection between the generalized parton distribution $E(x,0,t)$ and the Sivers asymmetry. For transversely polarized nucleon targets, generalized parton distributions are asymmetric in impact parameter space. This impact parameter space asymmetry, together with the final state interaction of the active quark, gives rise to the Sivers asymmetry in momentum space. We demonstrate this phenomenon explicitly in the scalar diquark model. This result also illustrates the physics that underlies the correlation between the anomalous magnetic moment and the Sivers asymmetry for a given quark flavor.