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arXiv · 2610.22994

Leading-twist proton parton distribution amplitude from scalar and axial-vector diquark correlations

B. Almeida-Zamora·L. Albino·C. Mezrag·J. Segovia
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Abstract

We compute the leading-twist proton parton distribution amplitude (PDA) using algebraic representations of the nucleon Faddeev wave function inspired by perturbation-theory integral representations. The PDA is obtained from a light-front projection of the covariant quark--diquark Faddeev amplitude and analysed in terms of its scalar- and axial-vector-diquark components. We derive analytic expressions for the corresponding diquark distribution amplitudes and their contributions to the proton PDA. The resulting distribution is broad and concave, with its maximum $(x_1,x_2,x_3)\approx(0.55,0.20,0.25)$ displaced from the symmetric configuration $(1/3,1/3,1/3)$, which corresponds to the maximum of the perturbative-QCD asymptotic form. Scalar-diquark correlations generate a strong asymmetry in the longitudinal momentum distribution, whereas axial-vector correlations redistribute momentum among the valence quarks and significantly reduce this asymmetry. We calculate low-order Mellin moments and obtain a compact parametrisation of the proton PDA at the hadronic scale, $μ_0=0.51\,\mathrm{GeV}$. We then perform the leading-order QCD evolution of its normalized shape to $μ=2\,\mathrm{GeV}$, finding that evolution reduces the momentum asymmetry while preserving a clear imprint of the non-perturbative quark--diquark correlations. The results provide insight into the role of such correlations in shaping the proton light-front structure and furnish non-perturbative input for studies of hard exclusive baryonic processes.

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B. Almeida-Zamora, L. Albino, C. Mezrag, J. Segovia. 2026-10-16. Leading-twist proton parton distribution amplitude from scalar and axial-vector diquark correlations. https://arxiv.org/abs/2610.22994

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