Leading twist nuclear shadowing, nuclear generalized parton distributions and nuclear DVCS at small x

We generalize the leading twist theory of nuclear shadowing and calculate quark and gluon generalized parton distributions (GPDs) of spinless nuclei. We predict very large nuclear shadowing for nuclear GPDs. In the limit of the purely transverse momentum transfer, our nuclear GPDs become impact-parameter-dependent nuclear parton distributions (PDFs). Nuclear shadowing induces nontrivial correlations between the impact parameter b and the light-cone fraction x. We make predictions for the deeply virtual Compton scattering (DVCS) amplitude and the DVCS cross section on Pb-208 at high energies. We calculate the cross section of the Bethe-Heitler (BH) process and address the issue of the extraction of the DVCS signal from the e A \to e \gamma A cross section. We find that the e A \to e \gamma A differential cross section is dominated by DVCS at the momentum transfer t near the minima of the nuclear form factor. We also find that nuclear shadowing leads to dramatic oscillations of the DVCS beam-spin asymmetry, A_{LU}, as a function of t. The position of the points where A_{LU} changes sign is directly related to the magnitude of nuclear shadowing.Comment: 37 pages, 12 figures. Matches the published version, Phys. Rev. 79, 035210 (2009

Semiclassical solution to the BFKL equation with massive gluons

In this paper we proceed to study the high energy behavior of a scattering amplitudes in the Yang-Mills theory with the Higgs mechanism for the gauge boson mass. The spectrum of the $j$-plane singularities of the $t$-channel partial waves, and corresponding eigenfunctions of the BFKL equation in leading log approximation (LLA), were previously calculated by us numerically in arXiv:1401.4671 . Here we develop a semiclassical approach and investigate the influence of the impact parameter exponential decrease, existing in this model, on the high energy asymptotic behaviour of the scattering amplitude. This approach is much simpler than the numerical calculations, and reproduces our earlier numerical results. The analytical (semianalytical) solutions which have been found in this paper, can be used to incorporate correctly the large impact parameter behavior in the framework of CGC/saturation approach. This behaviour is interesting as provides the high energy amplitude for the electroweak theory, which can be measured experimentally.Comment: 22 pages, 13 Figure

Generalized parton distributions from neutrino experiments: twist-three effects

We study the twist-3 corrections to the neutrino induced deeply virtual meson production due to the chiral odd transversity Generalized Parton Distribution (GPD). We found that in contrast to pion electroproduction, in neutrino-induced processes these corrections are small. This occurs due to large contribution of unpolarized GPDs $H,\, E$ to the twist-2 amplitude in neutrinoproduction. Our results are important for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.Comment: 4 pages, 1 figure. Contribution to the proceedings of the 13th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU 2013), Sep 30-Oct 4, Rome, Italy. Details of evaluation may be found in arXiv:1401.154