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Finite-Gap CMV Matrices: Periodic Coordinates and a Magic Formula

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<mark>Journal publication date</mark>30/09/2021
<mark>Journal</mark>International Mathematics Research Notices
Issue number18
Volume2021
Number of pages70
Pages (from-to)14016-14085
Publication StatusPublished
Early online date13/02/20
<mark>Original language</mark>English

Abstract

We prove a bijective unitary correspondence between (1) the isospectral torus of almost-periodic, absolutely continuous CMV matrices having fixed finite-gap spectrum E and (2) special periodic block-CMV matrices satisfying a Magic Formula. This latter class arises as E-dependent operator Möbius transforms of certain generating CMV matrices that are periodic up to a rotational phase; for this reason we call them "MCMV."Such matrices are related to a choice of orthogonal rational functions on the unit circle, and their correspondence to the isospectral torus follows from a functional model in analog to that of GMP matrices. As a corollary of our construction we resolve a conjecture of Simon; namely, that Caratheodory functions associated to such CMV matrices arise as quadratic irrationalities.

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