Analytic continuation of concrete realizations and the McCarthy Champagne conjecture

Abstract

In this paper, we give formulas that allow one to move between transfer function type realizations of multi-variate Schur, Herglotz and Pick functions, without adding additional singularities except perhaps poles coming from the conformal transformation itself. In the two-variable commutative case, we use a canonical de Branges-Rovnyak model theory to obtain concrete realizations that analytically continue through the boundary for inner functions which are rational in one of the variables (so-called quasi-rational functions). We then establish a positive solution to McCarthy's Champagne conjecture for local to global matrix monotonicity in the settings of both two-variable quasi-rational functions and d-variable perspective functions. Contents 1. Introduction 1.1. Overview 1.2. Background 1.3. Summary of results 2. Two-variable realization formulae 3. Boundary behavior of quasi-rational functions 4. Some algebraic identities 4.1. The block 2 by 2 matrix inverse formula Date: September 30, 2020.