Nucleon form factors and dispersion relations

We define a dispersive technique, based on data, analyticity and dispersion relations to handle the nucleon form factors. Two applications are explicitly considered. In the first case, we use the available theoretical and experimental information on the ratio between the electric and magnetic proton form factors, as inputs in the dispersive procedure that gives a complex description of this ratio in the whole q2 complex plane. In the second case, by inverting a dispersion relation and considering the data and the pQCD asymptotic behaviour as inputs, the magnetic nucleon form factors are reconstructed in their unphysical region. Resonances and phases in agreement with the expectations are found. (orig.)