Time- and Spacelike Nucleon Electromagnetic Form Factors beyond Relativistic Constituent Quark Models

For the first time, a phenomenological analysis of the experimental electromagnetic form factors of the nucleon, both in the timelike and spacelike regions, is performed by taking into account the effects of nonvalence components in the nucleon state, within a light-front framework. Our model, based on suitable Ansatzes for the nucleon Bethe-Salpeter amplitude and a microscopic version of the well-known Vector Meson Dominance model, has only four free parameters (determined by the spacelike data with $\chi^2/datum \sim 1.7$), and yields a nice description of the experimental electromagnetic form factors in the physical region in the range $-30 (GeV/c)^2 < q^2 < 20 (GeV/c)^2$, except for the neutron one in the timelike region. Valuable information can be gained in the timelike region on possible missing Vector Mesons around $q^2 \sim 4.5 (GeV/c)^2$ and $q^2 \sim 8.0 (GeV/c)^2