Electromagnetic form factors for nucleons and pions at positive and negative q(2) in the model of quark-gluon strings

The electromagnetic form factors for pions and nucleons are considered with in the model of quarkgluon strings, where the momentum-transfer dependence of hadronic form factors is determined by the intercepts of the correspondi ng Regge trajectories and by the Sudakov form factor. Analytic expressions found for form factors in the timelike region admit an analytic continuatio n to the spacelike region. The resulting form factors for pions and nucleon s comply well with experimental data both for positive and for negative val ues of the squared momentum transfer q(2). It is shown that the distinction s 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 negat ive 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 i s proposed in the present study makes it possible to describe fairly well a vailable experimental data on the Pauli form factor F-2 and on the ratio G( e)/G(m). (C) 2000 MAIK "Nauka/Interperiodica".