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We present a new determination of the generalized parton distributions (GPDs) with their uncertainties at zero skewness, $ \xi =0 $, through a simultaneous analysis of all available experimental data of the nucleon electromagnetic form factors (FFs), nucleon charge and magnetic radii, proton axial FFs (AFFs) and wide-angle Compton scattering (WACS) cross sections for the first time, and we investigate whether there is any tension between these data. This can be considered the most comprehensive analysis of GPDs at $ \xi=0 $ performed so far. We show that such an analysis provides the simultaneous determination of three kinds of GPDs, namely $ H^q $, $ \widetilde{H}^q $ and $ E^q $, considering also the sea-quark contributions. As a result, we find that the inclusion of the WACS and AFF data at larger values of the momentum transfer squared $ Q^2=-t $ can put new constraints on GPDs and change them drastically in some cases. We show that there is a considerable tension between the WACS and the proton magnetic form factor ($ G_M^p $) data, especially at larger values of $ -t $. However, we indicate that the results for the gravitational FF $ M_2 $ and the proton total angular momentum $ J^p $ calculated using the extracted GPDs are in relatively good agreement with the light-cone QCD sum rules (LCSRs) and lattice QCD predictions when the sea-quark contributions are considered and both WACS and $ G_M^p $ data are included in the analyses simultaneously., Comment: 36 pages, 33 figures, and 6 tables; Accepted for publication in Physical Review D

We determine the valence generalized parton distributions (GPDs) $ H_v^q $ and $ E_v^q $ with their uncertainties at zero skewness by performing a $ \chi^2 $ analysis of the world electron scattering data considering two-photon exchange corrections. The data include a wide and updated range of the electric and magnetic form factors (FFs) of the proton and neutron. As a result, we find that there are no enough constraints on GPDs $ E_v^q $ from FFs data solely though $ H_v^q $ are well constrained. By including the new data of the charge and magnetic radius of the nucleon in the analysis, we show that they put new constraints on the final GPDs, especially on $ E_v^q $. Moreover, we calculate the gravitational FF $ M_2 $ and the total angular momentum $ J^q $ using the extracted GPDs and compare them with the FFs obtained from the light-cone QCD sum rules (LCSR) and Lattice QCD. We show that our results are interestingly in a good consistency with the pure theoretical predictions., Comment: 20 pages, 13 figures, and 5 tables

We study the kaon leptoproduction on the basis of the handbag approach. We consider the leading-twist contribution together with the transversity twist-3 effects which were found to be important in the description of pseudo-scalar meson production. We present our predictions for the cross section and spin asymmetries in the kaon leptoproduction., 4 pages, 4 figures. Talk at the 20th International Symposium on Spin Physics (SPIN2012) JINR, Dubna, Russia September 17 - 22, 2012. To be publish in Proceedings

We analyze electroproduction of light vector mesons (V=rho, phi and omega) at small Bjorken-x in the handbag approach in which the process factorizes into general parton distributions and partonic subprocesses. The latter are calculated in the modified perturbative approach where the transverse momenta of the quark and antiquark forming the vector meson are retained and Sudakov suppressions are taken into account. Modeling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal cross sections at large photon virtualities. The results are in fair agreement with the findings of recent experiments performed at HERA and HERMES., 27 pages, 20 figures, using LATEX with graphicx

Based on previous studies of hard exclusive leptoproduction of pions in which the essential role of the pion pole and the transversity generalized parton distributions has been pointed out, we present predictions for the four partial cross sections of the exclusive Drell-Yan process, pi^-p -> l^-l^+n., SCOAP3

The role of transversity or helicity-flip generalized parton distributions (GPDs) in leptoproduction of vector mesons is investigated within the framework of the handbag approach. The transversity GPDs in combination with twist-3 meson wave functions, occur in the amplitudes for transitions from a transversely polarized virtual photon to a longitudinal polarized vector meson. The importance of the transversity GPDs can be examined in some of the spin density matrix elements and in transverse target spin asymmetries. Using suitable parametrizations of both helicity-flip and non-flip GPDs, which are essentially taken from our previous papers, we estimate these observables and compare the results with available data., Comment: 30 pages, 19 figures

Exploiting a set of generalized parton distributions (GPDs) derived from analyses of hard exclusive leptoproduction of rho0, phi and pi+ mesons, we investigate the omega spin density matrix elements (SDMEs) recently measured by the HERMES collaboration. It turns out from our study that the pion pole is an important contribution to omega production. It will be treated as a one-particle exchange since its evaluation from the GPD E-tilde considerably underestimates its contribution. As an intermediate step of our analysis we extract the pi-omega transition form factor for photon virtualities less than 4 GeV^2. From our approach we achieve results for the omega SDMEs in good agreement with the HERMES data. The role of the pion pole in exclusive rho0 and phi leptoproduction is discussed too., Comment: 27 pages, 33 figures

Double spin asymmetries in the diffractive $Q \bar Q$ and $J/\Psi$ leptoproduction are discussed. It is shown that the asymmetries for longitudinally polarized lepton and longitudinally or transversely polarized proton can be used to study spin dependent gluon distribution of the proton at small $x$., Comment: 8 pages, latex, 4 figures, talk at the Iternational Workshop "Symmetry and Spin", Prague-Spin2000, Prague, July 17 - 22, 2000. To be published in proceedings

We calculate the double spin asymmetry of the diffractive Q $$\bar Q$$ and vector meson leptoproduction at COMPASS energies. We analyze dependences of the asymmetry on the structure of the Pomeron-proton coupling. It is shown that it is difficult to study the spin structure of the Pomeron coupling with the proton from the A ll asymmetry. The A lT asymmetry might be an appropriate object for this investigation.

We calculate the cross section and \(A_{\mathrm{ll}}\) asymmetry of the diffractive J/\(\Psi\) leptoproduction for a simple model of a Pomeron coupling with a proton, which contains the \(\gamma^{\alpha}\) term and a spin-dependent part. It is shown that the asymmetry caused by the Pomeron coupling \(\propto \gamma^{\alpha}\) does not vanish for nonzero \(|t|\). The sensitivity of the polarized diffractive J/\(\Psi\) production to the spin-dependent part of the Pomeron coupling is found to be rather weak. As a result, it is difficult to study the structure of the Pomeron coupling with the proton in future polarized diffractive experiments on the J/\(\Psi\) production.

We analyse the diffractive $Q \bar Q$ production and final jet kinematics in polarized deep-inelastic lp scattering at $\sqrt{s}=20 GeV$. We show that this reaction can be used in the new spectrometer of the COMPASS Collaboration at CERN to study the quark-pomeron coupling structure., Comment: 10 pages, latex, 6-Ps figures

Transverse single spin asymmetry in polarized diffractive $Q\overline{Q}$ production is calculated. It is shown that this asymmetry strongly depends on the spin structure of the Pomeron coupling, which permits one to study the Pomeron coupling properties in future polarized experiments.

Theoretical predictions for the behavior of the slope of nucleon-nucleon scattering and another parameters of the differential cross-sections in the framework of dynamic model are compared with the recent UA4/2 data at small transfer momenta and at the centerof-mass energy of 541 GeV. The predictions at superhigh energies are considered.

We analyze light meson electroproduction within the handbag model, where the amplitude factorizes into Generelized Parton Distributions (GPDs) and a hard scattering part. The cross sections and spin asymmetries for various vector and pseudoscalar mesons are analyzed. We discuss what information on hadron structure can be obtained from GPDs., Latex, 14 pages, 12 figures, Presented at the 5th joint International HADRON STRUCTURE '11 Conference, June 27- July 1, 2011, Tatranska Strba (Slovak Republic)

Estimates for electroproduction of pseudoscalar mesons at small values of skewness are presented. Cross sections and asymmetries for these processes are calculated within the handbag approach which is based on factorization in hard parton subprocesses and soft generalized parton distributions (GPDs). The latter are constructed from double distributions. Transversity GPDs are taken into account; they are accompanied by twist-3 meson wave functions. For most pseudoscalar-meson channels a combination of H-tilde_T$ and E-bar_T$ plays a particularly prominent role. This combination of GPDs which we constrain by moments obtained from lattice QCD, leads with the exception of the pi+ and eta' channels, to large transverse cross sections., Comment: 36 pages and 27 figures

On the basis of the QCD model at large distances, the author analyses the qq-sea contribution to the spin effects in the s to infinity , t-fixed limit. It is shown that such effects lead to the spin-flip amplitude increasing as s. The magnitude of spin-flip and spin-nonflip amplitudes is estimated within simple nonperturbative models for quark and gluon propagators. The relative role of spin effects from the wavefunction and the elementary quark subprocess is also discussed. It is shown that the quark-sea effects in the scattering amplitude can reach 30-40% of the contribution of the simple two-gluon exchange at small momenta transfer.

The spin-flip amplitudes of the meson-nucleon and nucleon-nucleon scattering are calculated in the framework of the dynamic model taking into account the interactions at large distances. The consideration of the strong form factors at the corresponding vertex and prea-symptotic contributions allowed us to describe correctly the differential cross sections and spin effects of hadron-hadron scattering at high energies. On this basis predictions at high and superhigh energies are made.

On the basis of QCD at large distances with taking account of some nonperturbative properties of the theory, the possibility of spin-flip effects in high energy hadron processes at fixed momenta transfer is investigated.

The target asymmetry for electroproduction of vector mesons is investigated within the handbag approach. While the generalized parton distribution (GPD) H is taken from a previous analysis of the elctroproduction cross section, we here construct the GPD E from double distributions and constrain it by the Pauli form factors of the nucleon, positivity bounds and sum rules. Predictions for the target asymmetry are given for various vector mesons and discussed how experimental data on the asymmetry will further constrain E and what we may learn about the angular momenta the partons carry., 24 pages, 11 figures, latex

We study light vector meson electroproduction at small $x$ within the generalized parton distributions (GPDs) model. The modified perturbative approach is used, where the quark transverse degrees of freedom in the vector meson wave function and hard subprocess are considered. Our results on the cross section and spin observables are in good agreement with experiment, 6 pages, 5 figures, presented at Symmetries and Spin meeting, Prague, 8- 14 July, 2007

We analyze electroproduction of light vector mesons at small Bjorken-x in an approach that includes the gluonic generalized parton distributions and a partonic subprocess, gamma g --> (q q-bar) g, q q-bar --> V. The subprocess is calculated to lowest order of perturbative QCD taking into account the transverse momenta of the quark and antiquark as well as Sudakov suppressions. Our approach allows to investigate the transition amplitudes for all kind of polarized virtual photons and polarized vector mesons. Modelling the generalized parton distributions through double distributions and using simple Gaussian wavefunctions for the vector mesons, we compute the longitudinal and transverse cross sections at large photon virtualities as well as the spin density matrix elements for the vector mesons. Our results are in fair agreement with the findings of recent experiments performed at HERA., 40 pages, 22 figures (using LATEX), v2: beginning of Sect. 3 is rewritten, a discussion on alternative choices of the slopes included and further small improvements in text

It is reported on an analysis of vector meson leptoproduction at small Bjorken-$x$ and large photon virtuality within an approach that bases on generalized parton distributions (GPDs). This approach leads to results for cross sections and spin density matrix elements for $\rho$ and $\phi$ leptoproduction in fair agreement with experiment., Comment: Report at Spin 2004 Symposium, October 10-16, Trieste, Italy

We discuss quark-antiquark leptoproduction within a QCD two-gluon exchange model at small $x$. The double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive $Q \bar Q$ production are analysed at eRHIC energies. The predicted $A_{lT}$ asymmetry is large and can be used to obtain information on the polarized generalized gluon distributions in the proton.

We consider double spin asymmetries for longitudinally polarized leptons and transversely polarized protons in diffractive vector meson and $Q \bar Q$ production at high energies within the two-gluon model. The asymmetry predicted for meson production is quite small. The $A_{lT}$ asymmetry for $Q \bar Q$ production contains two independent terms which are large and can be used to obtain information on the polarized gluon distributions in the proton., Comment: 27 pages, latex, 13 figures, Chapter 7 was modified -calculation of new asymmetry was added, some typing error was corrected

We study spin asymmetries in diffractive $Q \bar Q$ and vector meson production which are sensitive to the spin-dependent part of the two-gluon-nucleon coupling. It is found that the $A_{ll}$ and $A_{lT}$ asymmetry in diffractive reactions can be used to study polarized gluon distributions of the proton., LaTex, 5 pages, 2 PS figures, to appear in Proc. of the 14th International Spin Physics Symposium, SPIN2000, Osaka, Japan, Oct. 16-21 2000

We study $pp$ scattering at high energies and moderately large momentum transfer, using a model in which the proton is viewed as being composed of a quark and a diquark. We show that this model leads to single and double spin transverse asymmetries which are neither small nor vanish at high energies., Comment: 19 pages, 9 PS figures. Final version of the paper, published in Phys. Rev, D 60, 014019, 1999

In this report we calculate the cross section and $A_{ll}$ asymmetry for the diffractive $J/\Psi$ leptoproduction. We study dependences of the asymmetry on the structure of the Pomeron-proton coupling, Comment: 4 pages, latex, two PS figures, presented at the International Workshop "Symmetry and Spin" PRAHA'98

The intercept of the supercritical Pomeron is examined with the use of different forms of the scattering amplitudes of the bare Pomeron. The one-to-one correspondence between the eikonal phase and the ratio of the elastic and total cross section is shown. Based on new experimental data of the CDF Collaboration, the intercept and power of the logarithmic growth of the bare and total Pomeron amplitude are analyzed. It is shown that as a result of the eikonalization procedure, the bare QCD Pomeron becomes compatible with experiment., Comment: LaTex text of the article + 1 Fig.1 in LaTex form

The problems of transverse polarization in high energy hadron processes were discussed many times at the SPIN-PHYSICS conference (see [1,2] e.g.). It was noted that on the basis of perturbative QCD it is impossible to obtain the ratio of spin-flip and spin-non-flip amplitudes which do not vanish as s→∞. As a result, the transverse polarization effects go to zero with growing energy.

It is shown that the spin effects which do not decrease with energy are in agreement with the experiment. These spin effects are obtained in elastic quark‐quark scattering on the basis of QCD at large distances.