Poor man's scaling: XYZ Coqblin-Schrieffer model revisited

We derive the third-order poor man's scaling equation for a generic Hamiltonian describing a quantum impurity embedded into an itinerant electron gas. We show that the XYZ Coqblin-Schrieffer model introduced by one of us earlier is algebraically renormalizable in the sense that the form of the Hamiltonian is preserved along the scaling trajectory, write down the scaling equations for the model, and analyze the renormalization group flows in the cases of both constant and pseudogap densities of states.