Nuclear Theory·nucl-th

Tuesday·July 28, 2026

20 papers—14 primary·6 cross-listed

15
Effects of flavor-mixings on charged kaon and pion parton distribution functions
Fabio L. Braghin🇧🇷 · Parada T. P. Hutauruk🇯🇵
We investigate the charged kaon and pion parton distribution functions (PDFs) in the U(3) Nambu--Jona-Lasinio (NJL) model, considering a novel flavor-mixing interaction arising from vacuum polarization that differs from the instanton-induced 't~Hooft interaction. In this work, the proper-time regularization scheme is employed, and, effectively, it might take quark confinement into account. The gap equations, the meson masses, and the meson--quark coupling constants are calculated in the presence of flavor mixing interactions. The valence-quark distributions of the charged kaon and pion are calculated and compared with existing experimental data and JAM analysis results at scales $μ^{2} =$ 4 and 27 GeV $^{2}$ . The strength of mixing effects on the PDFs is found to be proportional to the quark effective masses and their differences. We further find that the dominant flavor mixing effects in the pion valence up-quark distribution at scales $μ^{2} =$ 27 and 4 GeV $^{2}$ are around $x ≃ 0.3$ and $x ≃ 0.8$ , while for the kaon, the effects are shown at around $x ≃ 0.2$ and $x ≃ 0.7$ . We also find similar strength of mixing effects on the PDFs at both scales $μ^{2} = 4$ and 27 GeV $^{2}$ ; however, it certainly improves the pion and kaon PDFs.
↳ hep-phhep-exhep-latnucl-th1 citation
16
Near-Light-Cone Nonhydrodynamic Structure from Boosted Hydrodynamics
Navid Abbasi🇨🇳 · Jewel Kumar Ghosh🇧🇩 · Dirk H. Rischke🇩🇪
Hydrodynamics provides a universal description of many-body systems at long wavelengths. Its long-lived collective excitations, known as hydrodynamic modes, admit long-wavelength expansions whose convergence is encoded in the analytic structure of retarded correlators of conserved quantities in thermal equilibrium. We show that a boost can change which nonhydrodynamic singularity limits such an expansion. In the large-boost limit, the relevant singularity originates in the large-momentum, near-light-cone region of the rest-frame spectrum. After factoring out the Lorentz-factor growth, the rescaled convergence scale is controlled by the microscopic spectral structure of the theory. We explicitly demonstrate this in two examples: relaxation-time kinetic theory and holography.
↳ hep-thgr-qcnucl-th0 citations
17
First constraints on the nonperturbative gluon Collins-Soper kernel
Artur Avkhadiev🇺🇸 · Yang Fu🇺🇸 · Phiala E. Shanahan🇺🇸 · Michael L. Wagman🇺🇸 · Yong Zhao🇺🇸
The gluon Collins-Soper kernel, which encodes the rapidity evolution of transverse-momentum-dependent gluon distributions, is constrained for the first time in the nonperturbative regime, for transverse momentum scales $q_{T} \in [300 MeV, 1.3 GeV]$ . The constraints are determined in lattice QCD at a close-to-physical pion mass $M_{π} = 172 (3) MeV$ , a single lattice spacing $a = 0.15 fm$ , and next-to-next-to-leading logarithmic matching in Large-Momentum Effective Theory. These results represent the first step toward a controlled determination of the gluon Collins-Soper kernel in QCD, with eventual phenomenological import and relevance to present and future experiments sensitive to the gluon structure of hadronic matter.
↳ hep-lathep-phnucl-th0 citations
18
Analytic decomposition of two-body electroweak processes with left-hand cuts
André Baião-Raposo🇩🇪 · Raúl A. Briceño🇺🇸 · Nicolas Lang🇪🇸 · Felipe G. Ortega-Gama🇺🇸 · Bianca Pol🇺🇸
We derive an on-shell representation for electroweak $2 + J \to 2$ transition amplitudes involving two hadrons in both the initial and final state for systems where there are left-hand singularities generated by light-particle exchange, e.g. one-pion exchange. The derivation treats the insertion of the electroweak current perturbatively, keeping only the leading-order contribution in the external field, while the hadronic interactions are treated to all orders, including one-particle exchange effects. We find that, in such processes, the amplitude can have logarithmic singularities, as well as one-particle pole singularities, due to these exchanges. We isolate those contributions, as well as previously identified triangle singularities. The result is expressed in terms of the purely hadronic amplitude, exchange-current kernels, triangle functions, and a class of short-distance transition functions that are real and smooth below unaccounted-for thresholds. While we consider only transitions with spinless particles, this work is an important step toward constraining form factors of systems involving nucleons or vector mesons in the heavy quark sector, where the one-pion-exchange singularity is quite close to threshold.
↳ hep-lathep-phnucl-th0 citations
19
Electromagnetic structure of charged and neutral strange vector mesons
Parada T. P. Hutauruk🇯🇵
We investigate the electromagnetic form factors (EMFFs) of the charged $K^{*+} (892)$ ( $u s ˉ$ ) and neutral $K^{0} (896)$ ( $d s ˉ$ ) strange vector mesons within the covariant Nambu--Jona-Lasinio (NJL) model, employing the Schwinger proper-time regularization scheme to regularize ultraviolet divergences while incorporating the QCD aspect of quark confinement. To this end, we evaluate the charge (electric) $G_{C} (Q^{2})$ , magnetic $G_{M} (Q^{2})$ , and quadrupole $G_{Q} (Q^{2})$ form factors, as well as the charge radii, of the charged $K^{+} (892)$ and neutral $K^{0} (896)$ strange vector mesons. We find the charge radii to be $⟨ r^{2} ⟩_{K^{+}} = 0.45 fm^{2}$ and $⟨ r^{2} ⟩_{K^{0}} = - 0.04 fm^{2}$ , respectively, while the corresponding magnetic moments are $μ_{K^{+}} = 2.67, μ_{N}$ and $μ_{K^{* 0}} = 0.032, μ_{N}$ . These results are consistent with other theoretical calculations and lattice QCD simulations.
↳ hep-phnucl-th0 citations
20
Symbolic Extraction of Non-Perturbative Transverse-Momentum-Dependent Distributions from Drell-Yan Data
Cole Granger🇺🇸 · Alessandro Bacchetta🇮🇹 · Valerio Bertone🇫🇷 · Chiara Bissolotti🇺🇸 · Matteo Cerutti🇫🇷 · Marco Radici🇮🇹 · Simone Rodini🇮🇹 · Lorenzo Rossi🇮🇹 · Cristiano Fanelli🇺🇸
We present an analytical parametrization of the non-perturbative transverse-momentum-dependent (TMD) parton distribution function of unpolarized quarks, extracted from Drell-Yan data using a combination of neural-network fitting and symbolic regression. A factorized neural network is trained directly against experimental cross-section data from fixed-target, Tevatron, RHIC, and LHC experiments at next-to-next-to-next-to-leading logarithmic accuracy, and symbolic regression is subsequently applied to each network component to discover compact analytical expressions. The final formula is selected from a Pareto front in the space of expression complexity and experimental $χ^{2}$ , yielding a closed-form non-perturbative function with 9 free numerical constants that achieves $χ^{2} / ndf = 1.040$ over 482 data points. A non-trivial $x$ - $b_{T}$ cross term is retained even under a sparsity prior that biases it toward zero, indicating a mild but genuine correlation between the longitudinal momentum fraction and the transverse momentum. This work demonstrates that symbolic regression is a viable tool for bridging flexible machine-learning fits and interpretable analytical TMD parametrizations, and opens a systematic path toward data-driven discovery of specific features of non-perturbative QCD.
↳ hep-phnucl-thphysics.data-an0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Effects of flavor-mixings on charged kaon and pion parton distribution functions

Near-Light-Cone Nonhydrodynamic Structure from Boosted Hydrodynamics

First constraints on the nonperturbative gluon Collins-Soper kernel

Analytic decomposition of two-body electroweak processes with left-hand cuts

Electromagnetic structure of charged and neutral strange vector mesons

Symbolic Extraction of Non-Perturbative Transverse-Momentum-Dependent Distributions from Drell-Yan Data

Affiliations