Hadronic structure on the light front. I. Instanton effects and quark-antiquark effective potentials

This is the first of a sequence of papers that addresses the nonperturbative origin of the central and spin-dependent forces between quarks. Its main thrust is a focus on meson spectroscopy in the center-of-mass frame. We suggest a novel ``dense instanton ensemble'' model for the QCD vacuum, to explain the interquark forces in mesons, from quarkonia to heavy-light and light-light ones. The sequels will show how to export these interactions to the light front, and derive the corresponding Hamiltonians, mesonic, and baryonic light front wave functions. The ultimate aim of the series is to bridge the gap between hadronic spectroscopy and partonic observables.