AN INTRINSIC 1 N EXPANSION FOR MANY-FERMION SYSTEMS/

The 1/N expansion is a popular tool for investigating non-perturbative long-range phenomena. In many-body models, discretization of the Ferm i surface naturally introduces a many-component picture. If, for examp le, number symmetry is broken, N almost-equal-to (exp [1/lambda])(d-1) , where lambda > 0 is the bare coupling constant. We expect that this intrinsic 1/N expansion appears whenever the <<free propagator>> of th e system is singular along a hypersurface (for instance, in the Anders on model for localized and extended states).