2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/82513Using the Funtional Integrals Formulation is developes a self-consistent mean field expansion to evolution operators of a system composed by two subsystems. This is a general expansion and can be generalized for more of two subsystems, which can be as system composed by fermions and bosons with an interaction between their ($σ$-model , $σ-ω$ model or maser model) as a fermionic system with two or more different interactions between fermions particles, (NJL model ).34 pages in LATEX, 2 figuresNuclear Theorytext