Summary
VMD models fail in their descriptions of nucleon and nuclear form factors, not because they are wrong but because they are incomplete. The version of quark-hadron duality which they express, the so-calledQ 2-duality, refers only to the spectrum of vector mesons which couple to the photon. This version is incomplete. Quark-hadron duality includes also thes-channel or Bloom-Gilman duality which allows to reproduce asymptotic quark model behavioure.g. in structure functions, by summing over the contributions of hadronic, not only vector meson, intermediate states. A VMD model which incorporates these two forms of duality is presented. It gives excellent fits to nucleon form factors in the spacelike region. When the corresponding formulae are continued to the timelike region they yield absolute predictions. Those for the proton agree remarkably well with the available data. The proton and neutron form factors in this region turn out to be approximately of the same order for all values of the momentum transfer. We therefore predict approximately equal values for the cross-sections\(\sigma \left( {e^ + e^ - \to p\bar p} \right)\) and\(\sigma \left( {e^ + e^ - \to n\bar n} \right)\) for all values of the e+e− centre-of-mass energy.
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Etim, E., Malecki, A. Nucleon form factors in a VMD model with bothQ 2- andS-channel duality. Nuov Cim A 104, 531–543 (1991). https://doi.org/10.1007/BF02813589
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DOI: https://doi.org/10.1007/BF02813589