2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/5471We present the Green's functions that are the solutions of the massive Klein-Gordon equation for a scalar field with non-minimal coupling to gravitation for several static and expanding cosmological models. An important feature of such functions is that they can be used to study the appearence of a Casimir energy in models of the universe with compact spatial sections.8 pages, revtex4, no figuresAstrophysicsGeneral Relativity and Quantum Cosmologytext