  The extended Lomon-Gari-Kr\"umpelmann model of nucleon electromagnetic form
factors, which embodies \rho, \rho', \omega, \omega' and \phi vector meson
contributions and the perturbative QCD high momentum transfer behavior has been
extended to the time-like region. Breit-Wigner formulae with momentum-dependent
widths have been considered for broad resonances in order to have a
parametrization for the electromagnetic form factors that fulfills, in the
time-like region, constraints from causality, analyticity, and unitarity. This
analytic extension of the Lomon-Gari-Kr\"umpelmann model has been used to
perform a unified fit to all the nucleon electromagnetic form factor data, in
the space-like and time-like region (where form factor values are extracted
from e+e- <-> nucleon-antinucleon cross sections data). The knowledge of the
complete analytic structure of form factors enables predictions at extended
momentum transfer, and also of time-like observables such as the ratio between
electric and magnetic form factors and their relative phase.

High Energy Physics - Phenomenology