Electromagnetic form factors for nucleons and pions at positive and negative q2 in the model of quark-gluon strings

The electromagnetic form factors for pions and nucleons are considered within the model of quarkgluon strings, where the momentum-transfer dependence of hadronic form factors is determined by the intercepts of the corresponding Regge trajectories and by the Sudakov form factor. Analytic expressions found for form factors in the timelike region admit an analytic continuation to the spacelike region. The resulting form factors for pions and nucleons comply well with experimental data both for positive and for negative values of the squared momentum transfer q(2). It is shown that the distinctions between the absolute values of the pion and nucleon form factors F-pi(q(2)), G(m)(q(2)), and F-2(q(2)) at positive values of q(2) and those at negative values of this variable are associated with the analytic properties of the double-logarithmic term in the exponent of the Sudakov form factor. The spin structure of the amplitudes for quark transitions into hadrons that is proposed in the present study makes it possible to describe fairly well available experimental data on the Pauli form factor F-2 and on the ratio G(e)/G(m). (C) 2000 MAIK "Nauka/Interperiodica".