2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/137093This is a talk given on the $θ$vacuum and cluster properties and the non-linear sigma model proposed to be given on occasion of an invitation to the seventh international conference on Symmetry in Nonlinear Physics,June 24 - 30, 2007, Kiev.High Energy Physics - Theorytext