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arXiv · 2404.13245

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

Kiminad A. Mamo·Ismail Zahed
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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.

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Kiminad A. Mamo, Ismail Zahed. 2024-04-20. String-based parametrization of nucleon GPDs at any skewness: a comparison to lattice QCD. https://doi.org/10.1103/physrevd.110.114016

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