Poor man's scaling and Lie algebras

We consider a general model, describing a quantum impurity with degenerate energy levels, interacting with a gas of itinerant electrons, derive general scaling equation for the model, and analyse the connection between its particular forms and the symmetry of interaction. On the basis of this analysis we write down scaling equations for the Hamiltonians which are the direct products of su(3) Lie algebras and have either SU(2) × U(1) or SU(2) symmetry. We also put into a new context anisotropic Coqblin—Schrieffer models proposed by us earlier. (paper)