2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/172298This manuscript has been withdrawn, since the authors have detected numerical inaccuracies that invalidate their main results concerning the existence of repulsive Casimir forces within a rectangular piston. Formulas presented in the manuscript keep still valid. The authors deeply apologize for this mistake.4 pages, 5 figuresQuantum Physicstext