168 citations · 614 across the 54 of their papers we have counts for
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On the index of meromorphic operator-valued functions and some applications
Jussi Behrndt, Fritz Gesztesy, Helge Holden +1
We revisit and connect several notions of algebraic multiplicities of zeros of analytic operator-valued functions and discuss the concept of the index of meromorphic operator-value…
On Factorizations of Analytic Operator-Valued Functions and Eigenvalue Multiplicity Questions
Fritz Gesztesy, Helge Holden, Roger Nichols
We study several natural multiplicity questions that arise in the context of the Birman-Schwinger principle applied to non-self-adjoint operators. In particular, we re-prove (and e…
The Damped String Problem Revisited
Fritz Gesztesy, Helge Holden
We revisit the damped string equation on a compact interval with a variety of boundary conditions and derive an infinite sequence of trace formulas associated with it, employing me…
Algebro-Geometric Solutions of a Discrete System Related to the Trigonometric Moment Problem
Jeffrey S. Geronimo, Fritz Gesztesy, Helge Holden
We derive theta function representations of algebro-geometric solutions of a discrete system governed by a transfer matrix associated with (an extension of) the trigonometric momen…
Borg-Type Theorems for Matrix-Valued Schrödinger Operators
Steve Clark, Fritz Gesztesy, Helge Holden +1
A Borg-type uniqueness theorem for matrix-valued Schrödinger operators is proved. More precisely, assuming a reflectionless potential matrix and spectrum a half-line ,…
Trace formulae and inverse spectral theory for Schrödinger operators
Fritz Gesztesy, Helge Holden, Barry Simon +1
We extend the well-known trace formula for Hill's equation to general one-dimensional Schrödinger operators. The new function , which we introduce, is used to study absolutely c…