CORRECCIONES RADIATIVAS COUPLING CONSTANTS COUPLING EXPANSION CROMODINAMICA CUANTICA ENERGY SPECTRUM EQUILIBRIUM Electric resistance HAMILTONIANO Kondo effect LAGRANGIANA LANGEVIN EQUATION LIOUVILLE THEOREM Magnetic materials QUANTIZATION QUANTUM MECHANICS STOCHASTIC PROCESS TEORIAS DE MEDIDA EN LA RED WILSON LOOP Charge transport Cluster approximations Discretizations Embedded clusters Exact diagonalization Exact methods Finite clusters Finite sizes Finite systems Finite-size analysis Finite-size effects Ground-state densities