Non-factorized genuine twist 3 in exclusive electro-production of vector mesons

We present an analysis of genuine twist-3 quark contributions to the amplitude of exclusive electro-production of transversely polarized vector mesons. Using the formalism based on the momentum representation we calculated all the genuine twist-3 terms of quark contributions to gamma_T^* --> rho_T amplitude. We found that these terms can not be factorized owing to the existence of the infrared divergencies in the amplitude of hard sub-processes.Comment: 4 pages. Talk presented by I.V. Anikin at European Workshop on the QCD Structure of the Nucleon (QCD-N'02), Ferrara, Italy, 3-6 Apr 2002 (to appear in Nucl. Phys. A, Proc. Suppl.

Constraining gluon poles

In this letter, we revise the QED gauge invariance for the hadron tensor of Drell-Yan type processes with the transversely polarized hadron. We perform our analysis within the Feynman gauge for gluons and make a comparison with the results obtained within the light-cone gauge. We demonstrate that QED gauge invariance leads, first, to the need of a non-standard diagram and, second, to the absence of gluon poles in the correlators $\langle\bar\psi\gamma_\perp A^+\psi\rangle$ related traditionally to $dT(x,x)/dx$. As a result, these terms disappear from the final QED gauge invariant hadron tensor. We also verify the absence of such poles by analysing the corresponding light-cone Dirac algebra.Comment: 5 pages, 2 figures. The improved version. Accepted for publication in PL

New contributions to gluon poles in direct photon production

We consider the direct photon production in two hadron collision with one of the hadrons being transversely polarized. By using the contour gauge for gluon fields, we find that there are new twist-$3$ terms present in the hadron tensor of the considering process in addition to the standard twist-$3$ terms. In this work, we demonstrate that the significance of these new terms are two-fold: first, they are crucial to both the QED and QCD gauge invariance and, second, their contributions to the hadron tensor are at least the same as those from the standard ones. We also study the resuting effects which are responsible for the universality breaking of the corresponding twist-$3$ parton distributions.Comment: 19 pages, 5 figure

Search for isotensor exotic meson and twist 4 contribution to γ∗γ→ρρ\gamma^*\gamma\to\rho\rho

We present a theoretical estimate for the cross-section of exclusive $\rho^+\rho^-$ and $\rho^0\rho^0$-meson production in two photon collisions when one of the initial photons is highly virtual. We focus on the discussion of the twist 4 contributions which are related to the production of an exotic isospin 2 resonance of two $\rho$ mesons. Our analysis shows that the recent experimental data obtained by the L3 Collaboration at LEP can be understood as a signal for the existence of an exotic isotensor resonance with a mass around $1.5 {\rm GeV}$.Comment: 8 pages, 5 figure

Do L3 data indicate the existence of an isotensor meson ?

The QCD analysis of the hard exclusive production of $\rho^+\rho^-$ and $\rho^0\rho^0$ mesons in two photon collisions shows that the recent experimental data obtained by the L3 Collaboration at LEP can be understood as a signal for the existence of an exotic isotensor resonance with a mass around $1.5 {\rm GeV}$.Comment: 3 pages, 2 figures; Presented at Photon2005, Warsaw, Polan