From hard exclusive meson electroproduction to deeply virtual Compton scattering

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 parametrizations of the GPDs and describe its use in the handbag approach of the aforementioned hard scattering processes. We observe a 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.Comment: 37 pages, 12 figures v2 : fixed typos, updated to future published version (EPJC). v3 : fixed typo in Eq. (59

Pion’s valence-quark GPD and its extension beyond DGLAP region

We briefly report on a recent computation, with the help of a fruitful algebraic model, sketching the pion valence dressed-quark generalized parton distribution and, very preliminary, discuss on a possible avenue to get reliable results in both Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) and Efremov-Radyushkin-Brodsky-Lepage (ERBL) kinematial regions.This work has been partially supported by Spanish ministry projects FPA-2011-23781 and FPA-2014-53631- C2-2-P and French GDR 3034 PH-QCD “Cromodynamique Quantique et Physique des Hadrons" and ANR-12- MONU-0008-01 “PARTONS". We thank for their very valuable remarks to L. Chang, C.D. Roberts, F. Sabatié and S.M. Schmidt. H. M. and J. R-Q. are grateful for the chance to participate in the “21st Conference on Few-Body Problems in Physics", held in Chicago, and specially to C.D. Roberts for his warm hospitality at the Argonne National Laboratory

Accessing pion GPDs through the Sullivan process: is it feasible?

Describing hadronic structure is one of the most intriguing problems in physics. In this respect, generalized parton distributions (GPDs) constitute an outstanding tool, allowing to draw “three dimensional pictures” of hadron’s inside. Starting from contemporary models for pion’s GPDs fulfilling all constraints imposed by QCD, we compute Compton form factors of pions subjected to deeply virtual Compton scattering. We show CFF’s behaviour to be gluon-dominated at EIC’s kinematics. Finally we evaluate lepton-beam-spin asymmetries in the Sullivan process, demonstrating the existence of such and thus triggering optimism about the possibility of probing pion’s 3D structure at electron-ion colliders

The strong coupling constant at small momentum as an instanton detector

We present a study of $\alpha_{MOM}(p)$ at small p computed from the lattice. It shows a dramatic $\propto p^4$ law which can be understood within an instanton liquid model. In this framework the prefactor gives a direct measure of the instanton density in thermalised configurations. A preliminary result for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure

Pion and kaon structure at the electron-ion collider

Understanding the origin and dynamics of hadron structure and in turn that of atomic nuclei is a central goal of nuclear physics. This challenge entails the questions of how does the roughly 1GeV mass-scale that characterizes atomic nuclei appear; why does it have the observed value; and, enigmatically, why are the composite Nambu-Goldstone (NG) bosons in quantum chromodynamics (QCD) abnormally light in comparison? In this perspective, we provide an analysis of the mass budget of the pion and proton in QCD; discuss the special role of the kaon, which lies near the boundary between dominance of strong and Higgs mass-generation mechanisms; and explain the need for a coherent effort in QCD phenomenology and continuum calculations, in exa-scale computing as provided by lattice QCD, and in experiments to make progress in understanding the origins of hadron masses and the distribution of that mass within them. We compare the unique capabilities foreseen at the electron-ion collider (EIC) with those at the hadron-electron ring accelerator (HERA), the only previous electron-proton collider; and describe five key experimental measurements, enabled by the EIC and aimed at delivering fundamental insights that will generate concrete answers to the questions of how mass and structure arise in the pion and kaon, the Standard Model's NG modes, whose surprisingly low mass is critical to the evolution of our Universe

Contributions Numériques à l'Etude des Fonctions de Green et des Propriétés du Vide de la Chromodynamique Quantique

Michel Davier, Président - Georges Grunberg, Rapporteur - Laurent Lellouch, Rapporteur - Olivier Pène - Claude Roiesnel, Directeur de thèse - Klaus SchillingThis thesis provides a lattice evaluation of the coupling constant of Quantum Chromodynamics (QCD) in Landau gauge, in ``Momentum Substraction''-like renormalisation schemes (MOM), from a non-perturbative computation of the three-gluon vertex. This work was achieved with two flavours of Wilson dynamical quarks. It takes place in a scientific program which already contains a similar analysis in the framework of the ``pure gauge'' theory. In both cases, interpreting numerical data requires the introduction of a -condensate using the technics of the operator-product expansion (OPE). The contribution of this power correction is non-negligible till 10 GeV in the ``pure gauge'' case, but taking it into account gives a satisfactory agreement between the set of ``quenched'' as well as ``unquenched'' results with experimental data. Otherwise, this work also suggests a physical mechanism creating a -condensate in the framewok of a model of instanton gaz or liquid. Moreover, this picture allows to interpret the behaviour of the strong coupling constant in the deep infra-red region in a consistent way.Cette thèse présente une évaluation sur réseau de la constante de couplage de la Chromodynamique Quantique (QCD) en jauge de Landau, dans des schémas de renormalisation de type ``Momentum Substraction'' (MOM), à partir du calcul non-perturbatif du vertex à trois gluons. Ce travail a été mené avec deux saveurs dégénérées de quarks de Wilson dynamiques. Il prend place au sein d'un programme scientifique comprenant déjà une analyse similaire dans le cadre de la théorie ``pure jauge''. Dans les deux cas, l'interprétation des données numériques requiert l'introduction d'un condensat au moyen des techniques de développement en produit d'opérateurs (OPE). La contribution de cette correction en puissance est non-négligeable jusqu'à 10 GeV dans le cas ``pure jauge'', mais sa prise en compte rend satisfaisant l'accord de l'ensemble des résultats ``quenched'' et ``unquenched'' avec les données expérimentales. Par ailleurs, ce travail propose aussi un mécanisme physique de création du condensat dans le cadre d'un modèle de liquide ou de gaz d'instantons. Cette image permet de plus d'interpréter de manière cohérente le comportement de la constante de couplage forte dans l'infra-rouge profond