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We analyze deeply virtual Compton scattering on pions projected for a future electron-ion collider and conveyed in the Sullivan process. The relevant amplitude is known to be parametrized by generalized parton distributions. Hence taking advantage of state-of-the-art models for them, supplemented with effective leading-order scale evolution, we evaluate the amplitude for the process to occur and examine the pion’s structure from the perspective of electron-ion colliders. We estimate the expected event-rates for the Sullivan process showing: first, that deeply virtual Compton scattering on pions may be measurable at forthcoming experimental facilities. Second, that gluons may be decisive in the description of pions, driving the behavior of the relevant amplitudes and modulating the expected event-rates. [ABSTRACT FROM AUTHOR]

We present the EpIC Monte Carlo event generator for exclusive processes based on generalised parton distributions. EpIC utilises the PARTONS framework, which provides a flexible software architecture and a variety of modelling options for the partonic description of the nucleon. The generator offers a comprehensive set of features, including simulation of a variety of exclusive processes and radiative corrections. It may be used both in the analysis of experimental data, as well as for impact studies, especially for the future electron-ion colliders. [ABSTRACT FROM AUTHOR]

We discuss the use of machine learning techniques in effectively nonparametric modelling of generalised parton distributions (GPDs) in view of their future extraction from experimental data. Current parameterisations of GPDs suffer from model dependency that lessens their impact on phenomenology and brings unknown systematics to the estimation of quantities like Mellin moments. The new strategy presented in this study allows to describe GPDs in a way fulfilling theory-driven constraints, keeping model dependency to a minimum. Getting a better grip on the control of systematic effects, our work will help the GPD phenomenology to achieve its maturity in the precision era commenced by the new generation of experiments. [ABSTRACT FROM AUTHOR]

The impact of potential future measurements of beam charge asymmetries on the current knowledge of Compton form factors is evaluated. Elaborating on the results of a global neural network fit to deeply virtual Compton scattering data, a Bayesian reweighting analysis quantifies the improved determination of the real part of the Compton form factor H . Such an improvement is particularly relevant for the experimental determination of the proton mechanical properties or for universality studies of generalized parton distributions through analyses of virtual Compton scattering in both spacelike and timelike regions. [ABSTRACT FROM AUTHOR]

A unique feature of generalised parton distributions is their relation to the QCD energy–momentum tensor. In particular, they provide access to the mechanical properties of the proton i.e. the distributions of pressure and shear stress induced by its quark and gluon structure. In principle the pressure distribution can be experimentally determined in a model-independent way from a dispersive analysis of deeply virtual Compton scattering data through the measurement of the subtraction constant. In practice the kinematic coverage and accuracy of existing experimental data make this endeavour a challenge. Elaborating on recent global fits of deeply virtual Compton scattering measurements using artificial neural networks, our analysis presents the current knowledge on this subtraction constant and assesses the impact of the most frequent systematic assumptions made in this field of research. This study will pave the way for future works when more precise data will become available, e.g. obtained in the foreseen electron-ion colliders EIC and EIcC. [ABSTRACT FROM AUTHOR]

In the framework of collinear QCD factorization, the leading twist scattering amplitudes for deeply virtual Compton scattering (DVCS) and timelike Compton scattering (TCS) are intimately related thanks to analytic properties of leading and next-to-leading order amplitudes. We exploit this welcome feature to make data-driven predictions for TCS observables to be measured in near future experiments. Using a recent extraction of DVCS Compton form factors from most of the existing experimental data for that process, we derive TCS amplitudes and calculate TCS observables only assuming leading-twist dominance. Artificial neural network techniques are used for an essential reduction of model dependency, while a careful propagation of experimental uncertainties is achieved with replica methods. Our analysis allows for stringent tests of the leading twist dominance of DVCS and TCS amplitudes. Moreover, this study helps to understand quantitatively the complementarity of DVCS and TCS measurements to test the universality of generalized parton distributions, which is crucial e.g. to perform the nucleon tomography. [ABSTRACT FROM AUTHOR]

We present a novel approach to compute generalized parton distributions within the lightfront wave function overlap framework. We show how to systematically extend generalized parton distributions computed within the DGLAP region to the ERBL one, fulfilling at the same time both the polynomiality and positivity conditions. We exemplify our method using pion lightfront wave functions inspired by recent results of non-perturbative continuum techniques and algebraic nucleon lightfront wave functions. We also test the robustness of our algorithm on reggeized phenomenological parameterizations. This approach paves the way to a better understanding of the nucleon structure from non-perturbative techniques and to a unification of generalized parton distributions and transverse momentum dependent parton distribution functions phenomenology through lightfront wave functions. [ABSTRACT FROM AUTHOR]

8 Result of constraining the ANN model using 200 points evaluated with the GK model [25-27] for sea quarks: x= case, positivity enforced, FD( , ) not shown. The original article can be found online at https://doi.org/10.1140/epjc/s10052-022-10211-5. [Extracted from the article]

We review recent works on the modelling of generalised parton distributions within the Dyson-Schwinger formalism. We highlight how covariant computations, using the impulse approximation, allows one to fulfil most of the theoretical constraints of the GPDs. Specific attention is brought to chiral properties and especially the so-called soft pion theorem, and its link with the Axial-Vector Ward-Takahashi identity. The limitation of the impulse approximation are also explained. Beyond impulse approximation computations are reviewed in the forward case. Finally, we stress the advantages of the overlap of lightcone wave functions, and possible ways to construct covariant GPD models within this framework, in a two-body approximation. [ABSTRACT FROM AUTHOR]

Deeply virtual Compton scattering in the near forward kinematic region is the golden access to Generalized Parton Distributions. We studied the $${\mathcal{O}(\alpha_S)}$$ corrections to the scattering amplitude for both spacelike and timelike kinematics relevant respectively to the leptoproduction of a real photon and to the photoproduction of a lepton pair. It turns out that these corrections are phenomenologically important and that the gluonic contributions are by no means negligible, even in the moderate energy range of JLab12 and of the COMPASS-II experiment at CERN. [ABSTRACT FROM AUTHOR]

We systematically evaluate observables for hard exclusive electroproduction of real photons and compare them to experiment using a set of Generalized Parton Distributions (GPDs) whose parameters are constrained by Deeply Virtual Meson Production data, nucleon form factors and parton distributions. The Deeply Virtual Compton Scattering amplitudes are calculated to leading-twist accuracy and leading order in QCD perturbation theory while the leptonic tensor is treated exactly, without any approximation. This study constitutes a check of the universality of the GPDs. We summarize all relevant details on the parameterizations of the GPDs and describe its use in the handbag approach of the aforementioned hard scattering processes. We observe good agreement between predictions and measurements of deeply virtual Compton scattering on a wide kinematic range, including most data from H1, ZEUS, HERMES, Hall A and CLAS collaborations for unpolarized and polarized targets when available. We also give predictions relevant for future experiments at COMPASS and JLab after the 12 GeV upgrade. [ABSTRACT FROM AUTHOR]

The HERMES Collaboration has recently published a set of (correlated) beam charge, beam spin and target spin asymmetries for the Deeply Virtual Compton Scattering (DVCS) process. This reaction allows in principle to access the Generalized Parton Distributions (GPDs) of the nucleon. We have fitted, in the QCD leading-order and leading-twist handbag approximation, but in a model-independent way, this set of data and we report our results for the extracted Compton form factors. In particular, we are able to extract constrains on the H GPD. [ABSTRACT FROM AUTHOR]

The extraction of Compton form factors (CFFs) in a global analysis of almost all deeply virtual Compton scattering (DVCS) proton data is presented. The extracted quantities are DVCS sub-amplitudes and the most basic observables which are unambiguously accessible from this process. The parameterizations of CFFs are constructed utilizing the artificial neural network technique allowing for an important reduction of model dependency. The analysis consists of such elements as feasibility studies, training of neural networks with the genetic algorithm and a careful regularization to avoid over-fitting. The propagation of experimental uncertainties to extracted quantities is done with the replica method. The resulting parameterizations of CFFs are used to determine the subtraction constant through dispersion relations. The analysis is done within the PARTONS framework. [ABSTRACT FROM AUTHOR]

We propose new parameterizations for the border and skewness functions appearing in the description of 3D nucleon structure in the language of generalized parton distributions (GPDs). These parameterizations are constructed in a way to fulfill the basic properties of GPDs, like their reduction to parton density functions and elastic form factors. They also rely on the power behavior of GPDs in the x→1 limit and the propounded analyticity property of Mellin moments of GPDs. We evaluate compton form factors (CFFs), the sub-amplitudes of the deeply virtual compton scattering (DVCS) process, at the leading order and leading twist accuracy. We constrain the restricted number of free parameters of these new parameterizations in a global CFF analysis of almost all existing proton DVCS measurements. The fit is performed within the PARTONS framework, being the modern tool for generic GPD studies. A distinctive feature of this CFF fit is the careful propagation of uncertainties based on the replica method. The fit results genuinely permit nucleon tomography and may give some insight into the distribution of forces acting on partons. [ABSTRACT FROM AUTHOR]

We describe the architecture and functionalities of a C++ software framework, coined PARTONS, dedicated to the phenomenology of Generalized Parton Distributions. These distributions describe the three-dimensional structure of hadrons in terms of quarks and gluons, and can be accessed in deeply exclusive lepto- or photo-production of mesons or photons. PARTONS provides a necessary bridge between models of Generalized Parton Distributions and experimental data collected in various exclusive production channels. We outline the specification of the PARTONS framework in terms of practical needs, physical content and numerical capacity. This framework will be useful for physicists - theorists or experimentalists - not only to develop new models, but also to interpret existing measurements and even design new experiments. [ABSTRACT FROM AUTHOR]