Diagrammatic Theory of Anderson Impurity Models: Fermi and Non-Fermi   Liquid Behavior
  We review a recently developed method, based on a pseudoparticle representation of correlated electrons, to describe both Fermi liquid and non-Fermi liquid behavior in quantum impurity systems. The role of the projection onto the physical Hilbert space and the impossibility of slave boson condensation are discussed. By summing the leading coherent spin and charge fluctuation processes in a fully self-consistent and gauge invariant way one obtains the correct infrared behavior of the pseudoparticles. The temperature dependence of the spin susceptibility for the single channel and two-channel Anderson models is calculated and found to agree well with exact results. 
Johann Kroha and Peter W\"olfle