RENORMALIZED PERTURBATION EXPANSIONS AND FERMI-LIQUID THEORY

We give a procedure for a renormalized perturbation expansion. It is demonstrated for the Anderson impurity model, but has wide potential application. To zero order it describes the Landau noninteracting quasiparticles. To first order in the renormalized interaction U it gives the exact thermodynamic results for low temperatures, and to second order gives the exact T2 coefficient for the resistivity. The approach is not restricted to the Fermi liquid regime and provides a framework for systematic corrections to Fermi liquid theory.