Dynamical gluon effects in twist-3 generalized parton distributions of the proton

TL;DR

This paper investigates the twist-3 generalized parton distributions of the proton using light-front wave functions, revealing the importance of quark-gluon correlations beyond the Wandzura--Wilczek approximation for understanding proton structure.

Contribution

It provides a systematic nonperturbative calculation of twist-3 GPDs including quark-gluon correlations, beyond the common Wandzura--Wilczek approximation, using the Basis Light-Front Quantization framework.

Findings

Computed twist-3 GPDs including genuine quark-gluon contributions.

Analyzed the impact on quark orbital angular momentum and spin-orbit correlations.

Provided insights relevant for future EIC and EicC measurements.

Abstract

Within the Basis Light-Front Quantization framework, we systematically investigate the subleading-twist (twist-3) generalized parton distributions (GPDs) of the proton's valence quarks beyond the Wandzura--Wilczek (WW) approximation. The twist-3 GPDs are not independent; through the equations of motion they decompose into a non-genuine contribution and a genuine twist-3 term. The latter encodes quark--quark--gluon correlations and involves interference between the light-front Fock sectors |qqq> and |qqqg>, which are typically neglected in the WW approximation. Using light-front wave functions obtained from diagonalizing the proton light-front Hamiltonian for its |qqq> and |qqqg> Fock components, we compute these GPDs via their overlap representations. To further explore their physical implications, we also evaluate several twist-3--related quantities, including the quark orbital angular momentum, the total quark spin contribution, and the quark spin--orbit correlation. Our results provide new nonperturbative input on higher-twist dynamics particularly multi-parton interference effects relevant for future measurements at the EicC and the EIC.