String-based axial and helicity-flip GPDs: a comparison to lattice QCD

TL;DR

This paper develops an analytic string-based model for nucleon GPDs that matches lattice QCD results, incorporates experimental data, and predicts moments for future experimental testing.

Contribution

It introduces a novel string-inspired analytic framework for GPDs that unifies conformal moments, lattice data, and experimental constraints.

Findings

Reproduces some lattice moments in the non-singlet sector.

Predicts sea quark and gluon polarized moments for future tests.

Provides GPDs in x space consistent with lattice QCD.

Abstract

We construct an analytic, string based representation of the nucleon's axial and helicity flip conformal moments of generalized parton distributions that holds for any skewness and for both the quark and gluon channels. The starting point is the Mellin Barnes resummation of the conformal partial wave expansion, where the moments are parametrized by open (Reggeon) and closed string (Pomeron) trajectories with slopes determined by experimental form factors and meson/glueball spectroscopy. The forward limits are fixed by the empirical unpolarized and polarized parton distributions. Polynomiality, crossing symmetry and support are satisfied by construction. After NLO DGLAP ERBL evolution to $\mu=2$ GeV our analytic framework (i) reproduces some of the currently available lattice moments of $\mathbb{E}$ and $\widetilde{\mathbb{H}}$ in the non singlet sector, (ii) predicts sea quark and gluon polarized moments that will be testable by forthcoming simulations and experiments at Jefferson Lab and the future EIC, and (iii) yields axial and helicity flip GPDs in $x$ space in reasonable agreement with lattice QCD.