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FIZIKA B 8 (1999) 2, 335-344
HARD EXCLUSIVE ELECTROPRODUCTION OF TWO PIONS AND THEIR RESONANCESM. V. POLYAKOV Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg
188350, Russia Received 11 January 1999; Accepted 7 June 1999We study the hard exclusive production of two pions in the virtual photon fragmentation region with various invariant masses including the resonance region. The amplitude is expressed in terms of two-pion light-cone distribution amplitudes (2pDA's). We derive dispersion relations for these amplitudes, which allows to fix them completely in terms of pp-scattering phases and a few low-energy subtraction constants determind by the effective chiral Lagrangian. Quantitative estimates of the resonance as well pp background DA's at low normalization point are made. We also prove a new soft-pion theorem relating two-pion DA's to the one-pion DA's. Crossing relations between 2pDA's and parton distributions in a pion are discussed. We demontrate that by studying the shape of the pp mass spectra (not absolute cross section!) in a diffractive electroproduction, one can extract the deviation of the meson (p,r, etc.) wave functions from their asymptotic form 6 z(1-z) and hence to get important information about the structure of mesons. We suggest an (alternative to Söding's) parametrization of pp spectra which is suitable for large photon virtuality. PACS numbers: 12.38.Lg, 13.60.Fz, 13.60.Le
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