# Complete asymptotic expansions of the spectral function for symbolic perturbations of almost periodic Schrödinger operators in dimension one

### Jeffrey Galkowski

University College London, UK

## Abstract

In this article we consider asymptotics for the spectral function of Schrödinger operators on the real line. Let $P\colon L^2(\mathbb{R})\to L^2(\mathbb{R})$ have the form

where $W$ is a self-adjoint first order differential operator with certain modified almost periodic structure. We show that the kernel of the spectral projector, $\mathbf{1}_{(-\infty,\lambda^2]}(P)$ has a full asymptotic expansion in powers of $\lambda$. In particular, our class of potentials $W$ is stable under perturbation by formally self-adjoint first order differential operators with smooth, compactly supported coefficients. Moreover, the class of potentials includes certain potentials with *dense pure point spectrum*. The proof combines the gauge transform methods of Parnovski–Shterenberg and Sobolev with Melrose's scattering calculus.

## Cite this article

Jeffrey Galkowski, Complete asymptotic expansions of the spectral function for symbolic perturbations of almost periodic Schrödinger operators in dimension one. J. Spectr. Theory 12 (2022), no. 1, pp. 105–142

DOI 10.4171/JST/396