Perturbative renormalization of multi-channel Kondo-type models

The poor man's scaling is extended to higher order by the use of the open-shell Rayleigh-Schrödinger perturbation theory. A generalized Kondo-type model with the SU(n)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}\end{document}SU(m) symmetry is proposed and renormalized to the third order. It is shown that the model has both local Fermi-liquid and non-Fermi-liquid fixed points, and that the latter becomes unstable in the special case of n=m=2. Possible relevance of the model to the newly found phase IV in CexLa1-xB6 is discussed.