GAUGE INVARIANCE INVARIANZA DE UN PATRON RENORMALIZACION RENORMALIZATION A renormalisation group technique for spin and gauge systems with topological excitations ESPIN POLOS DE REGGE REGGE POLES SPIN TOPOLOGIA TOPOLOGY Application of a modified mean-field method to a gauge-invariant variational calculation CLUSTER MODEL COUPLING CONSTANTS COUPLING EXPANSION DISPERSION RELATIONS ENERGY SPECTRUM EQUILIBRIUM ISING MODEL LANGEVIN EQUATION LIOUVILLE THEOREM MEAN-FIELD THEORY METODO DE LA MATRIZ DE TRANSFERERENCIA MODELO DE ISING NIVELES ENERGETICOS P STATES PARTICULAS DE POMERANCHUK POMERANCHUK PARTICLES QUANTIZATION QUANTUM MECHANICS