[en] In this work a model is proposed to simulate the photoproduction of pseudoscalar mesons ('PI' and K) on the nucleon at high energy. This model is based on the exchange of mesonic or baryonic Regge trajectories, it is gauge invariant and it uses a Feynman diagram formalism inspired from isobaric models. The measurements concerning the following reactions γp → nπ⁺, γn → pπ^-, γp → pπ⁰ and γn → nπ⁰ are reviewed and the new model is confronted to the experimental results. The model gives a reasonable and coherent description of these 4 reactions. The model has also been applied to the photoproduction of strange mesons and of Λ and Σ baryons and has been extrapolated at low energy to the threshold of the reaction, the model matches the results even up to E_γ = 2 GeV for differential cross-sections and recoil polarization. An attempt has been made to associate a Regge based description, which is valid with low transfers, with perturbative quantum chromodynamics which is valid with high transfers. The model relies on the saturation of trajectories in the high transfer region and on the counting laws that give the right variation of the cross-section. It seems that a model based on linear trajectories can be reliable up to 4 GeV. The domain of high transfer has been too little investigated to provide enough experimental data to validate the model. An experiment whose purpose is to study the photoproduction of φ at high transfer, is proposed. This experiment requires an accelerator with high useful cycle because of the smallness of the expected cross-section. The CEBAF (continuous electron beam accelerator facility) as well as the CLAS 4π detector is presented. The study of γp → pφ and γp → KΛ^* (1520) requires the discrimination of kaons from pions so the measurement of 180 ps as time resolution allows the feasibility of the experiment. (A.C.)

[en] We briefly review in the following the subject of the recently introduced Generalized Parton Distributions'. We first outline the general theoretical formalism, then its relations to experimental observables. We also review the existing and short-term future projects at the various experimental facilities concerned by this physics. Finally, we discuss the recently published data which look extremely promising for the development of this field. (author)

[en] We give predictions for the leading order amplitudes for deeply virtual Compton scattering and hard meson electroproduction reactions at large Q² in the valence region in terms of skewed quark distributions. We give first estimates for the power corrections to these leading order amplitudes. In particular, we outline examples of experimental opportunities to access the skewed parton distributions at the current high-energy lepton facilities : JLab, HERMES and COMPASS

[en] We estimate the leading order amplitude for exclusive Deeply Virtual Compton Scattering in terms of modelised skewed parton distributions. The influence of the skewedness variable is found non negligible. We also estimate the power corrections due to the intrinsic transverse momentum of the partons and find that the onset of scaling is in the range 2-10 GeV²

[en] Deeply virtual Compton scattering (DVCS) and the exclusive electroproduction of vector mesons (ρ⁰, ρ^±, ω, phi) and pseudoscalar mesons (π⁰, ρ^±, ...) in the Bjorken regime are sensitive to the recently introduced off-forward parton distributions. We calculate the leading order amplitudes for DVCS and hard meson electroproduction reactions in the valence region and use a model ansatz for the OFPD's to give estimates of observables relevant for experiments at COMPASS, HERMES and JLAB

[en] We discuss the links between Generalized Parton Distributions (GPDs) and elastic nucleon form factors. These links, in the form of sum rules, represent powerful constraints on parametrizations of GPDs. A Regge parametrization for GPDs at small momentum transfer, is extended to the large momentum transfer region and it is found to describe the basic features of proton and neutron electromagnetic form factor data. This parametrization is used to estimate the quark contribution to the nucleon spin

[en] We estimate the reaction mechanisms for the photoproduction of the Θ⁺(1540) resonance on the nucleon, through K and K* Regge exchanges. We compare the size of the cross sections for the γn → K^- Θ⁺ and γp → (bar K)⁰ Θ⁺ reactions, and investigate their sensitivity to the spin-parity assignments J^P = (1/2)^±, (3/2)^± for the Θ⁺ resonance. The model allows to estimate the cross sections corresponding with a given upper bound on the width of the Θ⁺. Within this model, the cross sections on the neutron are found to be around a factor 5 larger than the ones on the proton, due to the presence of charged K exchange for the reaction on a neutron target. Furthermore, the photon asymmetry is found to display a pronounced sensitivity to the parity of the Θ⁺, making it a very promising observable to help determining the quantum numbers of the Θ⁺ resonance

[en] We review and discuss briefly the recent experimental results on Deep Virtual Compton Scattering on the proton. With the variety of independent observables beginning to be available and, in some instances, some very high precision data, some first global analysis for this process can be started, based on dedicated fitter codes, aiming at revealing the Generalized Parton Distributions content of the nucleon

[en] We have developed a fitting code based on the leading-twist handbag Deep Virtual Compton Scattering (DVCS) amplitude in order to extract Generalized Parton Distribution (GPD) information from DVCS observables in the valence region. In a first stage, with simulations and pseudo-data, we show that the full GPD information can be recovered from experimental data if enough observables are measured. If only some of these observables are measured, valuable information can still be extracted, with certain observables being particularly sensitive to certain GPDs. In a second stage, we make a practical application of this code to the recent DVCS Jefferson Lab Hall-A data from which we can extract numerical constraints for the two H GPD Compton form factors. (orig.)

[en] The process γp→phip close to threshold is investigated focusing on the role played by the s- and u-channel nucleonic resonances. For this purpose, a recent quark model approach, based on the SU(6)·O(3) symmetry with an effective Lagrangian, is extended to the phi meson photoproduction. Another non-diffractive process, the t-channel π⁰ exchange, is also included. The diffractive contribution is produced by the t-channel Pomeron exchange. Contributions from non-diffractive s- and u-channel processes are found small in the case of cross sections and polarization observables at forward angles. However, backward angle polarization asymmetries show high sensitivity to this non-diffractive process. Different prescriptions to keep gauge invariance for the Pomeron exchange amplitudes are investigated. Possible deviations from the exact SU(6)·O(3) symmetry, due to the configuration mixing, are also discussed