arXiv subjects

Kemal Tezgin

Publications and source records attributed to Kemal Tezgin.

13 recordsLinked to original sources

arXiv2026

Generalized Parton Distributions: Phenomenology, Extraction, and Hadron Imaging

Generalized Parton Distributions (GPDs) provide a framework for investigating the correlated momentum and spatial structure of quarks and gluons in hadrons and for accessing fundamental properties such as angular momentum and the QCD energy-momentum tensor. In this review, we discuss the present status of GPD phenomenology, emphasizing the challenges involved in connecting deeply virtual exclusive measurements to the underlying partonic structure. We organize this problem in terms of two successive inverse problems: the extraction of Compton Form Factors (CFFs) from measured observables and the reconstruction of GPDs from the convolution integrals defining the CFFs. We review the theoretical description and phenomenological parametrizations of GPDs, current strategies for CFF and GPD extraction, and the role of lattice QCD, Bayesian inference, uncertainty quantification, and artificial intelligence, including neural networks and interpretable machine-learning approaches. We discuss the limitations of present determinations and the opportunities offered by the Jefferson Lab program, complementary exclusive processes, and the future Electron-Ion Collider. Finally, we consider how increasingly precise and multidimensional information, together with new statistical and AI methodologies, will transform GPD phenomenology in the emerging era of precision hadron imaging.

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arXiv2026

Spin resummation of heavy quarkonium photoproduction: from the gluonic gravitational form factors to the holographic pomeron

Exclusive heavy quarkonium photoproduction probes the proton's gluonic structure from near-threshold (fixed-spin exchanges, gravitational form factors) to high energies (reggeized dynamics). We construct a holographic QCD amplitude that resums the even spin-$j$ gluonic exchanges, with the spin-2 input fixed by lattice QCD GFFs. The new framework describes the $J/ψ$ cross section from JLab to HERA energies in a unified manner. It explains why the spin-2 exchange model for GFF extraction near threshold is not a controlled approximation and suggests how to improve it.

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arXiv2026

Neural Network Representation of Generalized Parton Distributions (NNGPD)

We present a neural-network-based framework for modeling generalized parton distributions, referred to as NNGPD, in which GPDs are represented as flexible functions constrained through physically motivated integral relations. In this approach, experimental and theoretical information is incorporated into the training procedure via loss functions enforcing convolution integrals that define Compton form factors, as well as Mellin moments related to generalized form factors accessible in lattice QCD. This formulation reflects the inverse-problem character of GPD phenomenology without assuming a specific functional ansatz. As a proof of concept, we benchmark the NNGPD framework using a phenomenological spectator-based GPD model, from which synthetic training data for Compton form factors and Mellin moments are generated. The neural network is trained solely on these aggregate observables, and the resulting GPDs are compared directly with the underlying model distributions in a closure-type test. We find that the neural-network representation reproduces the main features of the GPDs over the relevant kinematic domain, despite being constrained only by their integral projections. This study demonstrates the viability of neural-network representations of GPDs constrained by global physical observables and provides a basis for future phenomenological applications combining experimental measurements of deeply virtual Compton scattering, including those anticipated at the Electron Ion Collider, with lattice QCD inputs for Mellin moments and generalized form factors.

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arXiv2025

Updated flexible global parametrization of generalized parton distributions from elastic and deep inelastic inclusive scattering data

An updated flexible parametrization of the generalized parton distributions in the quark, antiquark and gluon sectors is presented using constraints from high precision electron nucleon deep inelastic scattering data, as well as from the $u$, $d$ quark and gluonic contributions to the nucleon electromagnetic elastic form factors. The latter include recently updated lattice QCD moment calculations. The generalized parton distributions in the vector sector are $H$ and $E$. We rigorously constrain the partonic components, $H_{u_v}$, $H_{d_v}$, $H_{\bar{u}}$, $H_{\bar{d}}$, $H_{\bar{s}}$ and $H_{g}$, and the analogous quantities for $E$, with proper uncertainty quantification. These distributions obey leading order perturbative QCD evolution equations in $α_S$. Parametric forms at the initial scale, $Q_o^2 = 0.58$ $\mathrm{GeV}^2$, for both quarks and gluon distributions are presented as a function of the relevant kinematic variables, namely, the parton momentum fraction, $x$, the skewness, $ξ$, and the invariant, $t$. We also present the Compton form factors entering the deeply virtual Compton scattering process in the kinematic regimes for both fixed target and electron-ion collider settings.

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arXiv2025

Resurgence of deformed genus-1 curves: A novel perturbative/nonperturbative relation

We present a new perturbative/nonperturbative (P/NP) relation that applies to a broader class of genus-1 potentials, including those that possess real and complex instantons parametrized by a deformation parameter, such as polynomial and elliptic potentials. Our findings significantly extend the scope of quantum mechanical systems for which perturbation theory suffices to calculate the contributions of nonperturbative effects to energy levels, with or without the need for a boundary condition, depending on the potential. We further provide evidence for our results by predicting the corrections to the large-order behavior of the perturbative expansion for the Jacobi SD elliptic potential using the early terms of the instanton fluctuations that satisfy the P/NP relation.

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arXiv2025

Study of deeply virtual Compton scattering at the future Electron-Ion Collider

This study presents the impact of future measurements of deeply virtual Compton scattering (DVCS) with the ePIC detector at the electron-ion collider (EIC), currently under construction at Brookhaven National Laboratory. The considered process is sensitive to generalized parton distributions (GPDs), the understanding of which is a cornerstone of the EIC physics programme. Our study marks a milestone in the preparation of DVCS measurements at EIC and provides a reference point for future analyses. In addition to presenting distributions of basic kinematic variables obtained with the latest ePIC design and simulation software, we examine the impact of future measurements on the understanding of nucleon tomography and DVCS Compton form factors, which are directly linked to GPDs. We also assess the impact of radiative corrections and background contribution arising from exclusive $π^0$ production.

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arXiv2024

Unified genus-1 potential and a parametric perturbative/nonperturbative relation

We study a parametric deformation of the unified genus-1 anharmonic potential and derive a parametric form of perturbative/nonperturbative (P/NP) relation, applicable across all parameter values. We explicitly demonstrate that the perturbative expansion around the perturbative saddle is sufficient to generate all the nonperturbative information in these systems. Our results confirm the known results in the literature, where the cubic and quartic anharmonic potentials are reproduced under extreme parameter values, and go beyond these known results by developing the nonperturbative function of real and complex instantons solely from perturbative data.

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arXiv2024

Chiral-odd GPDs in the bag model

A study of chiral-odd generalized parton distributions (GPDs) of the nucleon is presented in the bag model demonstrating that in this model all four chiral-odd GPDs are non-zero contrary to other claims in literature. The bag model results for the GPDs $H_T^q(x,ξ,t)$, $E_T^q(x,ξ,t)$, $\tilde{H}_T^q(x,ξ,t)$ agree with other models within a typical quark model accuracy. We present one of the few quark model calculations where polynomiality is satisfied and the sum rule $\int dx\,\tilde{E}_T^q(x,ξ,t)=0$ holds. We confront our results with predictions from the large-$N_c$ limit, and with lattice QCD calculations. We conclude that the bag model successfully catches the main features of chiral-odd GPDs.

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arXiv2022

2D energy-momentum tensor distributions of nucleon in a large-$N_c$ quark model from ultra-relativistic to non-relativistic limit

Form factors of the energy-momentum tensor (EMT) can be interpreted in certain frames in terms of spatial distributions of energy, stress, linear and angular momentum, based on 2D or 3D Fourier transforms. This interpretation is in general subject to "relativistic recoil corrections", except when the nucleon moves at the speed of light like e.g. in the infinite-momentum frame. We show that it is possible to formulate a large-$N_c$ limit in which the probabilistic interpretation of the nucleon EMT distributions holds also in other frames. We use the bag model formulated in the large-$N_c$ limit as an internally consistent quark model framework to visualize the information content associated with the 2D EMT distributions. In order to provide more intuition, we present results in the physical situation and in three different limits: by considering a heavy-quark limit, a large system-size limit and a constituent-quark limit. The visualizations of the distributions in these extreme limits will help to interpret the results from experiments, lattice QCD, and other models or effective theories.

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arXiv2020

Energy momentum tensor and the D-term in the bag model

The energy-momentum tensor (EMT) form factors pave new ways for exploring hadron structure. Especially the D-term related to the EMT form factor D(t) has received a lot of attention due to its attractive physical interpretation in terms of mechanical properties. We study the nucleon EMT form factors and the associated densities in the bag model which we formulate for an arbitrary number of colors Nc and show that the EMT form factors are consistently described in this model in the large-Nc limit. The simplicity of the model allows us to test in a lucid way many theoretical concepts related to EMT form factors and densities including recently introduced concepts like normal and tangential forces, or monopole and quadrupole contributions to the angular momentum distribution. We also study the D-terms of rho-meson, Roper resonance, other N* states and Delta-resonances. Among the most interesting outcomes is the lucid demonstration of the deeper connection of EMT conservation, stability, the virial theorem and the negative sign of the D-term.

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arXiv2019

Monopole and quadrupole contributions to the angular momentum density

The energy-momentum tensor form factors contain a wealth of information about the nucleon. It is insightful to visualize this information in terms of 3D or 2D densities related by Fourier transformations to the form factors. The densities associated with the angular momentum distribution were recently shown to receive monopole and quadrupole contributions. We show that these two contributions are uniquely related to each other. The quadrupole contribution can be viewed as induced by the monopole contribution, and contains no independent information. Both contributions however play important roles for the visualization of the angular momentum density.

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arXiv2017

Remark on the Dunne-Unsal relation in exact semi-classics

Recently, it is realized that non-perturbative instanton effects can be generated to all orders by perturbation theory around a degenerate minima via Dunne-Unsal relation in several quantum mechanical systems. In this work we verify the Dunne-Unsal relation for resonance energy levels of one-dimensional polynomial anharmonic oscillators. We show that the relation is applicable to cubic and quartic anharmonic oscillators which are genus one potentials. However for higher order (higher genus) anharmonic potentials the relation is not satisfied and is subject to a certain extension.

hep-th↗

arXiv2017

A resurgence analysis for cubic and quartic anharmonic potentials

In this work we explicitly show resurgence relations between perturbative and one instanton sectors of the resonance energy levels for cubic and quartic anharmonic potentials in one-dimensional quantum mechanics. Both systems satisfy the Dunne-Unsal relation and hence we are able to derive one-instanton non-perturbative contributions with the fluctuation terms to the energy merely from the perturbative data. We confirm our results with previous results obtained by Zinn-Justin et al.

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