Barry Simon
A Canonical Factorization for Meromorphic Herglotz Functions on the Unit Disk and Sum Rules for Jacobi Matrices
(34K, AMS-LaTeX)
ABSTRACT. We prove a general canonical factorization for meromorphic Herglotz functions on
the unit disk whose notable elements are that there is no restriction (other than interlacing) on
the zeros and poles for their Blaschke product to converge and there is no singular inner function.
We use this result to provide a significant simplification in the proof of Killip-Simon of
their result characterizing the spectral measures of Jacobi matrices, $J$, with $J-J_0$ Hilbert-Schmidt.
We prove a nonlocal version of Case and step-by-step sum rules.