Intrinsic Transverse Size Effect

Two recently proposed concepts to improve the perturbative calculation of exclusive amplitudes, gluonic radiative corrections (Sudakov factor) and confinement size effects (intrinsic transverse momentum) are combined to study the neutron magnetic form factor in the space-like region. We find that nucleon distribution amplitudes modelled on the basis of current QCD sum rules indicate overlap with the existing data at the highest measured values of momentum transfer. However, sizeable higher-order perturbative corrections (K-factor) and/or higher-twist contributions cannot be excluded, although they may be weaker than in the proton case.Comment: 12 pages LATEX, 4 figures as compressed uu-encoded PS-file, preprint University of Wuppertal WU-B-94-16, University of Bochum RUB-TPII-04/94 (some typos eliminated

What binds quarks together at different momentum scales? A conceptual scenario

The binding effects of quarks within hadrons are discussed in terms of the pion distribution amplitude over longitudinal momentum fractions. To understand the behavior of this quantity at different momentum scales, the concept of synchronization in complex systems has been employed. It is argued that at low momentum scales, the quarks get correlated by nonlocal quark/gluon condensates that cause an endpoint-suppressed, mainly bimodal structure of the pion distribution amplitude inferred from a sum-rule analysis. The mass generation mechanism, within the framework of Dyson-Schwinger equations, and evolution effects pull these two peaks back to the center to form at $Q^2\to\infty$ the asymptotic distribution amplitude which represents the most synchronized $\bar{q}q$ state.Comment: 5 pages, 3 figures embedded; v2 includes remarks on and references to AdS/QCD; v3 has 6 pages, new material on short-tailed platykurtic distribution amplitude and minor corrections and clarifications added; abstract extended and references update

New vistas of the meson structure in QCD from low to high energies

This talk presents issues pertaining to the quark structure of the pion within QCD, both from the theoretical and from the experimental point of view. We review and discuss the pion-photon transition form factor and the pion's electromagnetic form factor vs. corresponding experimental data from the CLEO Collaboration and the JLab. We also examine the extent to which recent high-precision lattice computations of the second moment of the pion's distribution amplitude conform with theoretical models. Finally, we include predictions for the azimuthal asymmetry of the $\mu^+$ distribution in the polarized $\mu$-pair-induced DY production employing various pion distribution amplitudes.Comment: 6 pages, 7 figures, 2 tables. Talk presented at International Workshop on e^+e^- collisions from Phi to Psi, Frascati, Italy, 7-10 April 2008. V2 is an exclusive HEP version which includes predictions from AdS/QCD. V3: typo in title correcte