Speaker
Description
Generalized parton distributions (GPDs) are accessible through experimental processes such as deep virtual Compton scattering (DVCS) and deep virtual meson production (DVMP). Extracting GPDs directly from Compton form factors is complicated by the inherent ambiguity of deconvolution when parametrizing GPDs directly in momentum fraction $x$-space using double distributions. To overcome this challenge, we propose parametrizing GPDs via conformal moments in $j$-space, which naturally satisfy the polynomiality condition mandated by Lorentz invariance and offer a clear physical interpretation in terms of spin-$j$ resonance exchanges in the $t$-channel. In this talk, which is based on PRL.133.241901 (2024) and PRD.110.114016 (2024), we introduce a novel string-inspired parametrization for nucleon quark and gluon GPDs, applicable across all skewness $\xi$. Our framework expresses conformal moments explicitly as combinations of skewness-independent nucleon spin-$j$ A-form factors and skewness-dependent nucleon spin-$j$ D-form factors. These structures emerge naturally from $t$-channel string exchanges within an anti-de Sitter (AdS) space, ensuring consistency with Lorentz invariance and unitarity. Leveraging empirical Mellin moments from existing parton distribution functions (PDFs), our approach establishes a unique mapping between conformal moments in $j$-space and GPDs in momentum fraction $x$-space at arbitrary skewness.
