Thresholds and more bands of A.C. spectrum for the Molchanov--Vainberg Schrödinger operator with a more general long range condition

Abstract

The existence of absolutely continuous (a.c.) spectrum for the discrete Molchanov-Vainberg Schrödinger operator $D+V$ on ${\ell }^2({\mathbb{Z}}^d)$, in dimensions $d\ge 2$, is further investigated for potentials $V$ satisfying the long range condition $n_i(V-{\tau }_i^{\kappa }V)(n)=O({\ln }^{-q}(|n|))$ for some $q>2$, $\kappa \in \mathbb{N}$ even, and all $1\le i\le d$, as $|n|\to \infty$. ${\tau }_i^{\kappa }V$ is the potential shifted by $\kappa$ units on the $i^{\text{th}}$ coordinate. In this article \textit{finite} linear combinations of conjugate operators are constructed. These lead to more bands of a.c.\ spectrum being found. However, the new bands of a.c. spectrum are justified mainly by graphical evidence because the coefficients of the linear combinations are obtained by numerical polynomial interpolation. At the same time, an infinitely countable set of thresholds is rigorously identified (these will be defined exactly in the article). We conjecture that the spectrum of $D+V$ in dimension 2 is void of singular continuous spectrum, and that consecutive thresholds constitute endpoints of a band of a.c. spectrum.