Hard exclusive meson production and nonforward parton distributions

Abstract

We present an analysis of twist-2, leading order QCD amplitudes for hard exclusive leptoproduction of mesons in terms of double/nonforward parton distribution functions. After reviewing some general features of nonforward nucleon matrix elements of twist-2 QCD string operators, we propose a phenomenological model for quark and gluon nonforward distribution functions. The corresponding QCD evolution equations are solved in the leading logarithmic approximation for flavor nonsinglet distributions. We derive explicit expressions for hard exclusive π 0 , η, and neutral vector meson production amplitudes and discuss general features of the corresponding cross sections. * Work supported in part by BMBF

Evolution and models for skewed parton distributions

“…The evolution of skewed parton distributions was studied numerically in refs. [15,16,12,14,17]. In this section, we perform the numerical evolution of SPDs using the algorithm described in the previous session and present the results illustrating evolution patterns for SPDs constructed using the factorized model (3.1) with different choices for the profile function h(x, α).…”

Helicity skewed quark distributions of the nucleon and chiral symmetry

“…(4.23, 4.24) the momentum dependence of the constituent quark mass, M (p 2 ) cuts the loop momentum p and thus regularizes the UV divergence. Let us note that expressions (4.23, 4.24) are explicitly symmetric under transformation ξ → −ξ what follows from charge conjugation symmetry[6,5].…”

A low-polarisation loss prism ring resonator

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