SEMINARIO       Wednesday, 1st October 2003 - h. 15:00  Aula AE-A1     P. Faccioli E.C.T. and INFN, Trento        "Non-perturbative contributions to the electro-magnetic structure of light hadrons"           Abstract Recent measurements of hard exclusive electro-magnetic reactions performed at Jefferson Laboratory (JLAB) have revealed that the perturbative regime of QCD is reached only at surprisingly high values of the momentum transfer. This implies that there are short-scale no-perturbative structures inside ordinary hadrons. Instantons are non-perturbative gauge configurations which dominate the path integral in the semi-classical limit, and generate an effective interaction between light quarks ('t Hooft interaction). We first present a recent analysis based on lattice QCD, which provides strong evidence for instanton-induced dynamics. Then we show that, by accounting for the contribution of such non-perturbative structures, it is possible to quantitatively explain the JLAB data on the pion and proton formfactors.