2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/205408Current theoretical studies on the $σ$ and $κ$ resonances are reviewed. It is emphasized that all evidences accumulated so far are consistent with the picture that the $σ$ meson is the chiral partner of the Nambu--Goldstone bosons in a linear realization of chiral symmetry.Invited plenary talk given at CHIRAL 2007, Nov. 13-16, 2007, RCNP, Osaka, JapanHigh Energy Physics - Phenomenologytext