Wandzura-Wilczek approximation for the twist-3 DVCS amplitude

We present a derivation of Wandzura-Wilczek (WW) like relations for skewed parton distributions. It is demonstrated for photon-pion scattering that the skewed twist-3 parton distributions contributing to the DVCS amplitude have discontinuities at the points $x=\pm\xi$ in the WW approximation. This may lead to a violation of factorisation for the twist-3 DVCS amplitude with transverse polarization of the virtual photon. We show, however, that the contribution of the divergencies to the scattering of a transversely polarized virtual photon affects DVCS observables only at order $1/Q^2$ and can be neglected at twist-3 accuracy. For the scattering of a longitudinally polarized photon the twist-3 amplitude is free of such divergencies.Comment: 9 pages, no figures (To appear in Phys. Lett. B

πη\pi\eta pair hard electroproduction and exotic hybrid mesons

We show that hard electroproduction is a promising way to study exotic hybrid mesons, in particular through the hybrid decay channel $H \to \pi\eta$. We discuss the $\pi\eta$ generalized distribution amplitude, calculate the production amplitude and propose a forward-backward asymmetry as a signal for the hybrid meson production.Comment: 4 pages, 1 figure, presented by I.V. Anikin at Xth International Conference "BARYONS'04", Palaiseau, Franc

Single spin asymmetries in γ∗γ→πππ\gamma^* \gamma \to \pi \pi \pi at large Q^2

The $\gamma^* \gamma \to \pi \pi \pi$ reaction is analysed in QCD at large photon virtuality Q and small hadronic mass W. Its amplitude factorizes in a $3 \pi$ generalized distribution amplitude and a hard subprocess $\gamma^* \gamma \to q \bar q$ or $\gamma^* \gamma \to g g$. The interference of this process with a Brehmsstrahlung process in e e or $e \gamma$ collisions gives rise to interesting single spin asymmetries, particularly when W is near the $\omega$ mass.Comment: LaTeX, 12 page

Crossing and Radon Tomography for Generalized Parton Distributions

The crossing properties of the matrix elements of non-local operators, parameterized by Generalized Parton Distribution, are considered. They are especially simple in terms of the Double Distributions which are common for the various kinematical regions. As a result, Double Distributions may be in principle extracted from the combined data in these regions by making use of the inverse Radon transform, known as a standard method in tomography. The ambiguities analogous to the ones for the vetor potential in the two-dimensional magneto-statics are outlined. The possible generalizations are discussed.Comment: LaTeX, 10 page

Extraction of the pion distribution amplitude from polarized muon pair production

We consider the production of muon pairs from the scattering of pions on longitudinally polarized protons. We calculate the cross section and the single spin asymmetry for this process, taking into account pion bound state effects. We work in the kinematic region where the photon has a large longitudinal momentum fraction, which allows us to treat the bound state problem perturbatively. Our predictions are directly proportional to the pion distribution amplitude. A measurement of the polarized Drell-Yan cross section thus allows the determination of the shape of the pion distribution amplitude.Comment: 13 pages, using revtex, two figures added separately as one uuencoded Z-compressed fil

Pomeron-Odderon interference effects in electroproduction of π+π−\pi^+ \pi^-

We review the results of our studies on the charge and the spin asymmetries in the electroproduction of $\pi^+ \pi^-$ which are the observables sensitive to the Pomeron-Odderon interference.Comment: 5 pages LATEX, Talk given by L.Sz. at the 9th Int. High-Energy Physics Conference QCD '02, Montpellier, France, 2-9th July 200

On exotic hybrid meson production in gamma* gamma collisions

We present a theoretical study of exotic hybrid meson (JPC=1-+) production in photon-photon collisions where one of the photons is deeply virtual, including twist 2 and twist 3 contributions. We calculate the cross section of this process which turns out to be large enough to imply sizeable counting rates in the present high luminosity electron-positron colliders. We emphasize theimportance of the pi eta decay channel for the detection of the hybrid meson candidate pi_1(1400) and calculate the cross section and the angular distribution for pi eta pair production in the unpolarized case. This angular distribution is a useful tool for disentangling the hybrid meson signal from the background. Finally, we calculate the single spin asymmetry associated with one initial longitudinally polarized lepton.Comment: 13 pages, 14 figure