Boundary conditions of Sturm-Liouville operators with mixed spectra

Abstract

We study bounds on averages of spectral functions corresponding to Sturm-Liouville operators on the half line for different boundary conditions. As a consequence constraints are obtained which imply existence of singular spectrum embedded in a.c. spectrum for sets of boundary conditions with positive measure and potentials vanishing in an interval [0, N]. These constraints are related to estimates on the measure of sets where the spectral density is positive. (C) 2003 Elsevier Inc. All rights reserved.