Spectral Estimates for Degenerate Critical Levels

Abstract

We establish spectral estimates at a critical energy level for h-pseudo-differential operators. Via a trace formula, we compute the contribution of isolated (nonextremum) critical points under a condition of "real principal type." The main result holds for all dimensions, for a singularity of any finite order and can be invariantly expressed in terms of the geometry of the singularity. When the singularities are not integrable on the energy surface the results are significative since the order w.r.t. h of the spectral distributions are bigger than in the regular setting.