String-based parametrization of nucleon GPDs at any skewness: a comparison to lattice QCD

TL;DR

This paper presents a novel string-based parametrization of nucleon GPDs at all skewness values, derived from t-channel string exchanges in AdS spaces, which accurately models various GPDs and aligns with lattice data.

Contribution

The authors introduce a model-independent, string-inspired parametrization of nucleon GPDs that satisfies polynomiality and is validated against lattice QCD results.

Findings

Accurately models singlet, non-singlet, isovector, and flavor-separated GPDs.

Aligns well with existing lattice data for isovector GPDs.

Uses only five parameters fixed from form factors.

Abstract

We introduce a string-based parametrization for nucleon quark and gluon generalized parton distributions (GPDs) valid at all skewness values. The conformal moments of the GPDs are expressed as sums of the spin-j nucleon A-form factor, and the skewness-dependent spin-j nucleon D-form factor. This representation, which fulfills the polynomiality condition (due to Lorentz invariance) and does not rely on model-specific assumptions, is derived from t-channel string exchanges in AdS spaces. The spin-j nucleon D-form factor is closely related to the the spin-j nucleon A-form factor. We use the Mellin moments from empirical parton distributions to model the spin-j nucleon A-form factors. Using only five Regge slope parameters, fixed from the electromagnetic and gravitational form factors, our string-based parametrization generates accurate singlet, non-singlet, isovector, and flavor-separated nucleon quark GPDs, along with symmetric nucleon gluon GPDs from their Mellin-Barnes integral representations. Our isovector nucleon quark GPD is in agreement with existing lattice data. Our string-based parametrization should facilitate the empirical extraction and global analysis of nucleon GPDs in exclusive processes, bypassing the deconvolution challenge.