Nuclear Theory·nucl-th

Monday·August 4, 2025

12 papers—5 primary·7 cross-listed

06
Pionic gluons from global QCD analysis of experimental and lattice data
William Good🇺🇸 · Patrick C. Barry🇺🇸 · Huey-Wen Lin🇺🇸 · W. Melnitchouk🇺🇸 · Alex NieMiera🇺🇸 · Nobuo Sato🇺🇸
We perform the first global QCD analysis of parton distribution functions (PDFs) in the pion, with lattice-QCD data on gluonic pseudo--Ioffe-time distributions fitted simultaneously with experimental Drell-Yan and leading neutron electroproduction data. Inclusion of the lattice results with parametrized systematic corrections significantly reduces the uncertainties on the gluon PDF at parton momentum fractions $x ≳ 0.2$ , revealing a higher gluon density in the pion at large $x$ than in the proton. The similar gluon momentum fractions in the pion and proton further suggests a relative suppression of the pion gluon density at small $x$ .
↳ hep-phhep-exhep-latnucl-th7 citations
07
Truncation uncertainties for accurate quantum simulations of lattice gauge theories
Anthony N. Ciavarella🇺🇸 · Siddharth Hariprakash🇺🇸 · Jad C. Halimeh🇩🇪 · Christian W. Bauer🇺🇸
The encoding of lattice gauge theories onto quantum computers requires a discretization of the gauge field's Hilbert space on each link, which presents errors with respect to the Kogut--Susskind limit. In the electric basis, Hilbert space fragmentation has recently been shown to limit the excitation of large electric fields. Here, we leverage this to develop a formalism for estimating the size of truncation errors in the electric basis. Generically, the truncation error falls off as a factorial of the field truncation. Examples of this formalism are applied to the Schwinger model and a pure U(1) lattice gauge theory. For reasonable choices of parameters, we improve on previous error estimates by a factor of 10^{306}.
↳ quant-phhep-lathep-phnucl-th20 citations
08
Variational Neural Network Approach to QFT in the Field Basis
Kevin Braga🇺🇸 · Nobuo Sato🇺🇸 · Adam P. Szczepaniak🇺🇸
We present a variational neural network approach for solving quantum field theories in the field basis, focusing on the free Klein-Gordon model formulated in momentum space. While recent studies have explored neural-network-based variational methods for scalar field theory in position space, a systematic benchmark of the analytically solvable Klein-Gordon ground state -- particularly in the momentum-space field basis -- has been lacking. In this work, we represent the ground-state wavefunctional as a neural network defined on a discretized set of field configurations and train it by minimizing the Hamiltonian expectation value. This framework enables direct comparison to exact analytic results for a range of key observables, including the ground-state energy, two-point correlators, expectation value of the field, and the structure of the learned wavefunctional itself. Our results provide quantitative diagnostics of accuracy and demonstrate the suitability of momentum space for benchmarking neural network approaches, while establishing a foundation for future extensions to interacting models and position-space formulations.
↳ hep-phnucl-thPLB(2026)·1 citation
09
Analytic Solution for the Helicity Evolution Equations at Small $x$ and Large $N_{c} & N_{f}$
Jeremy Borden🇺🇸 · Yuri V. Kovchegov🇺🇸
We construct an exact analytic solution of the revised small- $x$ helicity evolution equations, where the contributions of the quark-to-gluon and gluon-to-quark transition operators were newly included. These evolution equations are written in the large- $N_{c} & N_{f}$ limit and are double-logarithmic, resumming powers of $α_{s} ln^{2} (1/ x)$ . Here $N_{c}$ and $N_{f}$ are the numbers of quark colors and flavors, while $α_{s}$ is the strong coupling constant and $x$ is the Bjorken- $x$ variable. Using our solution, we obtain analytic expressions for the flavor singlet quark and gluon helicity parton distribution functions (PDFs) and for the $g_{1}$ structure function as double-inverse Laplace transforms. We also extract analytic expressions for the four DGLAP polarized anomalous dimensions $Δ γ_{q q}, Δ γ_{q G}, Δ γ_{Gq}$ , and $Δ γ_{GG}$ : these expressions resum powers of $α_{s} / ω^{2}$ to all orders at large- $N_{c} & N_{f}$ (with $ω$ the Mellin moment variable). We extract the leading small- $x$ growth of the helicity distributions, \begin{align} \Delta\Sigma(x,Q^2) \sim \Delta G(x,Q^2)\sim g_1(x,Q^2) \sim \left(\frac{1}{x}\right)^{\alpha_h}, \end{align} where the intercept $α_{h}$ satisfies an algebraic equation. We determine $α_{h}$ numerically for various values of $N_{c}$ and $N_{f}$ . We further obtain the explicit asymptotic expressions for the helicity distributions, which yield numerical values for the ratio of the gluon helicity PDF to the flavor singlet quark helicity PDF in the small- $x$ asymptotic limit (for different $N_{f} / N_{c}$ ). We find that all our predictions for polarized DGLAP anomalous dimensions are fully consistent with the existing finite-order calculations. Similar to the large- $N_{c}$ case, our intercept $α_{h}$ exhibits a very slight disagreement with the predictions made within the infrared evolution equations framework.
↳ hep-phnucl-thPRD(2026)·12 citations
10
Thermoelectric figure of merit and the deconfinement phase transition
Kamaljeet Singh🇮🇳 · Raghunath Sahoo🇮🇳
Thermoelectric phenomena are traditionally associated with the interconversion of thermal and electrical energy in many-body systems. In the context of high-temperature quantum chromodynamics (QCD) matter produced in relativistic heavy-ion collisions, thermoelectric responses can provide insight into the evolving microscopic dynamics and the redistribution of effective degrees of freedom across the phase transition region. In this work, for the first time, we present a phenomenological study of the thermoelectric figure of merit ($ ZT $) in hot QCD matter, with a particular focus on its behavior across the hadronic and quark-gluon plasma phases. Using model-based calculations for the electrical conductivity, Seebeck coefficient, and thermal conductivity, we analyze the temperature dependence of $ ZT $ and identify characteristic features near the QCD phase transition temperature. Our results indicate that $ ZT $ exhibits nontrivial behavior near the transition region, reflecting the changing transport properties and active degrees of freedom in the medium. This phenomenological study of the thermoelectric figure of merit provides a complementary perspective to traditional transport studies and may provide critical insights for advancing the understanding of QCD matter through the transition region.
↳ hep-phhep-exhep-thnucl-ex+1PLB(2026)·2 citations
11
$ψ (2 S)$ production in jets using NRQCD
Marston Copeland🇺🇸 · Lin Dai🇨🇳 · Yu Fu🇺🇸 · Jyotirmoy Roy🇺🇸
Based on recent data from LHCb, we study $ψ (2 S)$ production in jets using non-relativistic QCD (NRQCD) in conjunction with the Fragmenting Jet Function (FJF) and Gluon Fragmentation Improved Pythia (GFIP) formalisms. Similar to previous studies of $J / ψ$ production in jets, our results show that these formalisms offer a much better description of data than the default Pythia+NRQCD prediction. We compare and contrast the predictions from the FJF formalism and the GFIP approach. In addition, our results show that the distribution of $ψ (2 S)$ in jets is an excellent discriminator to test different predictions for the $ψ (2 S)$ LDMEs from various extractions. We find a large disparity between the predictions from three different collaborations, showing that a more precise extraction of the $ψ (2 S)$ LDMEs may be necessary.
↳ hep-phnucl-thJHEP(2026)·10 citations
12
String-based axial and helicity-flip GPDs: a comparison to lattice QCD
Florian Hechenberger🇺🇸 · Kiminad A. Mamo🇺🇸 · Ismail Zahed🇺🇸
We construct an analytic, string based representation of the nucleon's axial and helicity flip conformal moments of generalized parton distributions that holds for any skewness and for both the quark and gluon channels. The starting point is the Mellin Barnes resummation of the conformal partial wave expansion, where the moments are parametrized by open (Reggeon) and closed string (Pomeron) trajectories with slopes determined by experimental form factors and meson/glueball spectroscopy. The forward limits are fixed by the empirical unpolarized and polarized parton distributions. Polynomiality, crossing symmetry and support are satisfied by construction. After NLO DGLAP ERBL evolution to $μ = 2$ GeV our analytic framework (i) reproduces some of the currently available lattice moments of $E$ and $H$ in the non singlet sector, (ii) predicts sea quark and gluon polarized moments that will be testable by forthcoming simulations and experiments at Jefferson Lab and the future EIC, and (iii) yields axial and helicity flip GPDs in $x$ space in reasonable agreement with lattice QCD.
↳ hep-phnucl-thPRD(2025)·7 citations

Affiliations

first authorsco-authorsvia INSPIRE

Pionic gluons from global QCD analysis of experimental and lattice data

Truncation uncertainties for accurate quantum simulations of lattice gauge theories

Variational Neural Network Approach to QFT in the Field Basis

Analytic Solution for the Helicity Evolution Equations at Small x and Large Nc​&Nf​

Thermoelectric figure of merit and the deconfinement phase transition

ψ(2S) production in jets using NRQCD

String-based axial and helicity-flip GPDs: a comparison to lattice QCD

Affiliations

Analytic Solution for the Helicity Evolution Equations at Small $x$ and Large $N_{c} & N_{f}$

$ψ (2 S)$ production in jets using NRQCD