## Box approximation and related techniques in spectral theory

##### Abstract

This dissertation is concerned with various aspects of the spectral theory of differential and pseudodifferential operators. It consists of two chapters. The first chapter presents a study of a family of spectral shift functions [xi]r, each associated with a pair of self-adjoint Schrödinger operators on a finite interval (0, r). Specifically, we investigate the limit behavior of the functions [xi]r when the parameter r approaches infinity. We prove that an ergodic limit of [xi]r coincides with the spectral shift function associated with the singular problem on the semi-infinite interval. In the second chapter, we study the attractor of the dynamical system r [arrow] Ar, where Ar is the truncated Wiener-Hopf operator surrounded by operators of multiplication by the function e[superscript alpha/2] [absolute value of dot], [alpha][greater than] 0. We show that in the case when the symbol of the Wiener-Hopf operator is a rational function with two real zeros the dynamical system r [arrow] Ar possesses a nontrivial attractor of a limit-circle type.

##### Degree

Ph. D.