Dirichlet-to-Neumann Maps, Abstract Weyl-Titchmarsh $M$-Functions, and a Generalized Index of Unbounded Meromorphic Operator-Valued Functions

Jussi Behrndt, Fritz Gesztesy, Helge Holden +1

We introduce a generalized index for certain meromorphic, unbounded, operator-valued functions. The class of functions is chosen such that energy parameter dependent Dirichlet-to-N…