Linking Chiral and Topological Aspects of the Quark-quark Interaction, in Qcd∗

Understanding the light-quark dynamics at all scales is a fundamental and open problem, in high-energy physics. In particular, the improving our knowledge of the non-perturbative interaction at intermediate and short distances has become essential, in order to explain the results of recent experiments on pion and proton electro-magnetic formfactors, performed at Jefferson Laboratory . Indeed, these high-precision measurements have shown that the perturbative regime in QCD does not set-in until very large values of the momentum transfer (Q > 6 GeV ). The delay of the onset of the asymptotic regime implies that there are strong, short-scale nonperturbative interactions, inside ordinary hadrons. It is commonly accepted that the physics of the light-quark sector of QCD is strongly influenced by the dynamics responsible for the chiral symmetry breaking (CSB). The characteristic energy scale associated to such