The Szego Condition for Coulomb Jacobi Matrices

Abstract

A Jacobi matrix with $a_n\to 1$, $b_n\to 0$ and spectral measure $\nu'(x)dx + d\nu_{sing}(x)$ satisfies the Szeg\H o condition if $\int_{0}^\pi \ln \bigl[ \nu'(2\cos\theta) \bigr] d\theta$ is finite. We prove that if $a_n = 1 + \frac {\alpha}{n} + O(n^{-1-\eps})$ and $b_n = \frac {\beta}{n} + O(n^{-1-\eps})$ with $2\alpha \ge |\beta|$ and $\eps>0$, then the corresponding matrix is Szeg\H o.