14,899 research outputs found

    Exclusive two-photon annihilation at large energy or large virtuality

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    I review recent progress in the theory of gamma gamma annihilation into meson or baryon pairs at large energy, and of the process gamma* gamma* -> pi0 at large photon virtuality.Comment: 6 pages, 4 figures. Presented at PHOTON 2003, Frascati, Italy, 7-11 April 200

    Generalized parton distributions: recent results

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    I review progress on selected issues connected with generalized parton distributions. Topics range from the description of hard exclusive reactions to the spatial distribution of quarks in the nucleon and the contribution of their orbital angular momentum to the nucleon spin.Comment: 9 pages, 5 figures. To appear in the proceedings of the Particles and Nuclei International Conference (PANIC 05), Santa Fe, NM, USA, 24-28 Oct 200

    Elastic meson production and Compton scattering

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    I discuss recent progress in the theory of exclusive meson production and Compton scattering, focusing on hard-scattering factorization and on the dipole formalism.Comment: 15 pages. Talk given at the Ringberg Workshop on New Trends in HERA Physics 2001. v2: References adde

    Photon polarisation in diffractive deep inelastic scattering

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    The distribution of a suitably defined azimuthal angle in diffractive deep inelastic scattering contains information on the polarisation of the exchanged photon. In particular it allows one to constrain the longitudinal diffractive structure function. We investigate the potential of such bounds in general and for particular diffractive final states.Comment: 12 pages, LaTeX2e, 3 figures included using epsf.st

    Spin and other aspects of generalized parton distributions

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    I discuss how generalized parton distribution probe various aspects of QCD bound states. Topics include the interplay between transverse and longitudinal structure, quantum mechanical interference, orbital angular momentum, helicity flip, and higher-spin targets.Comment: 9 pages, 2 figures. Talk given at Pacific Spin 2001, Beijing, China, 8-13 Oct. 200

    Generalized parton distributions with helicity flip

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    We show that for both quarks and gluons there are eight generalized parton distributions in the proton: four which conserve parton helicity and four which do not. We explain why time reversal invariance does not reduce this number from eight to six, as previously assumed in the literature.Comment: 20 pages, 2 figure
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