2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/39816It is the purpose of the present manuscript to emphasize those aspects that make the scalar sector with vacuum quantum numbers rather unique. Chiral symmetry is the basic tool for our study together with a resummation of Chiral Perturbation Theory (CHPT) that stresses the role of unitarity but also allows one to include explicit resonance fields and to match with the CHPT expansion at low energies.8 pages,2 figures. Invited talk at the $σ$-meson workshop, Kyoto, June 2000High Energy Physics - PhenomenologyHigh Energy Physics - ExperimentNuclear Theorytext