Exploring twist-3 chiral even generalized parton distributions of light sea quarks in the proton using the light front model

TL;DR

The study develops a light-front proton model with a spin-1 spectator and a spin-1/2 active sea quark, using a soft-wall AdS/QCD-inspired wavefunction and CT18NNLO-informed parameters to explore twist-3 chiral-even GPDs of light sea quarks. By computing GPD overlaps at zero skewness, it identifies four surviving twist-3 GPDs and connects them to the forward function g_T(x), while examining sea-quark flavor asymmetries, the Burkhardt–Cottingham sum rule, and the sea contribution to orbital angular momentum. The results reveal flavor-dependent structures in x and Δ_T, a divergent small-x behavior for x g_T^{\bar{u}}(x) and BC-sum-rule violations due to truncation, and generally good agreement with some model comparisons for sea OAM. These findings provide qualitative insights into nonperturbative sea-quark correlations and motivate future work on nonzero skewness and higher Fock components relevant for DVCS/DVMP measurements at EIC/EicC.

Abstract

We develop a light-front model of the proton to investigate the twist-3 chiral-even generalized parton distributions (GPDs) of light sea quarks. In this framework, sea quarks are treated as spin-\(\frac{1}{2}\) active partons, while the remaining proton constituents are modeled as spin-1 spectators. The light-front momentum wave function, derived from the soft-wall AdS/QCD approach, is fitted to unpolarized parton distribution functions (PDFs) from the CETQ global analysis to constrain the model parameters. To further validate the model, we analyze the sea quark flavor asymmetry through the difference \(\bar{d}(x) - \bar{u}(x)\) and the ratio \(\bar{d}(x)/\bar{u}(x)\), achieving good agreement with known phenomenological trends. Using this fitted distribution, we compute the twist-3 chiral-even GPDs and examine their dependence on the transverse momentum transfer \(\boldsymbol{Δ_T}\) and the longitudinal momentum fraction \(x\). In addition, we evaluate the twist-3 chiral-even PDF \(g_T(x)\) within this framework. The contribution of sea quarks to the proton's orbital angular momentum is also investigated and compared with existing results in the literature.

Figures (8)

• Figure 1: Sea quark unpolarized PDFs in the proton are fitted to CT18NNLO data: panel $(a)$ shows the distribution for $x \bar{u}$, and panel $(b)$ shows $x \bar{d}$ in the kinematic region $0.0001 < x < 1$ at the scale $Q_0 = 2\, \text{GeV}$.
• Figure 2: The sea quark flavor asymmetry is illustrated in both panels. The left panel (a) shows the difference $\bar{d}(x) - \bar{u}(x)$, while the right panel (b) presents the ratio $\bar{d}(x)/\bar{u}(x)$. Experimental data from NuSea/E866 are depicted by red triangles, and data from SeaQuest/E906 are shown as green circles. The theoretical predictions from our model are represented by the blue curve.
• Figure 3: The twist-3 chiral-even GPDs of light sea quarks, corresponding to the Dirac structure $\Gamma = \gamma^i$, are presented. Panel (a) shows the distribution for the $\bar{u}$ quark, while panel (b) displays the corresponding distribution for the $\bar{d}$ quark.
• Figure 4: The twist-3 chiral-even GPDs of light sea quarks, corresponding to the Dirac structure $\Gamma = \gamma^i \gamma_5$, are plotted as functions of the longitudinal momentum fraction $x$ and transverse momentum transfer $\boldsymbol{\Delta}_T$ in the range $0.005 < x < 0.6$ and $0 < \boldsymbol{\Delta}_T < 2$ GeV.
• Figure 5: The twist-3 chiral-even generalized parton distribution (GPD) $x \tilde{E}_{2T}$, corresponding to the $\gamma^i$ Dirac structure, is plotted as a function of $x$ for fixed values of the transverse momentum transfer: $\boldsymbol{\Delta}_T = 0.1 \ \text{GeV}$ (blue), $0.9 \ \text{GeV}$ (red), and $1.8 \ \text{GeV}$ (black).