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).