Clock spacing for two-sided Jacobi matrices

Abstract

We study local eigenvalue spacing for finite truncations of a two-sided Jacobi matrix with two movable endpoints. In particular, we show that a suitable analog of clock spacing follows from a pointwise reflectionlessness condition. We obtain this as a consequence of a new scaling limit for Christoffel--Darboux kernels with a movable starting point. Without reflectionlessness, we obtain a new class of limit kernels, which combine distinct contributions from $\pm \infty$. We also show that clock spacing in the two-sided setting is a fragile phenomenon, which can be destroyed by the change of a single Jacobi coefficient; in particular, it is not merely a consequence of absolutely continuous spectrum.

19 pages