2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/41193I explain the concept that light quarks diffuse in the QCD vacuum following the spontaneous breakdown of chiral symmetry. I exploit the striking analogy to disordered electrons in metals, identifying, among others, the universal regime described by random matrix theory, diffusive regime described by chiral perturbation theory and the crossover between these two domains.Lectures given at the Cargese Summer School, August 6-18, 2001High Energy Physics - PhenomenologyDisordered Systems and Neural NetworksHigh Energy Physics - LatticeNuclear Theorytext