works on
Agler decomposition 1characteristic functions 1invariant subspaces 1kernel theory 1reproducing kernels 1

From the 1 of 5 linked papers with an AI index.

collaborators

5 papers

math.FA2026

When do Kernels Admit Characteristic Functions?

Caixing Gu, Shuaibing Luo, Georgios Tsikalas +1

The paper proves that a reproducing kernel admits a characteristic function exactly when a Beurling-type invariant subspace condition holds, and this condition can be expressed as…

math.FA2026

Beurling Criteria for Reproducing Kernels

Shuaibing Luo, Scott McCullough, Georgios Tsikalas

A classical theorem due to Beurling-Lax-Halmos characterizes the invariant subspaces of the unilateral shift as ranges of isometric multiplication operators acting on the Hardy spa…

math.FA2026

Spectral Estimates over Multiply Connected Domains

Georgios Tsikalas

We consider the quantum analogue of a disk with pairwise disjoint circular holes. We establish a uniform upper bound for the associated spectral constant that is independent of…

math.FA2026

Operators with small Kreiss constants

Nikolaos Chalmoukis, Georgios Tsikalas, Dmitry Yakubovich

We investigate matrices satisfying the Kreiss condition with lying arbitrarily close to We provide lower bo…

math.FA2025

The complete Pick property for pairs of kernels and Shimorin's factorization

Scott McCullough, Georgios Tsikalas

Let be a pair of Hilbert function spaces with kernels . In a 2005 paper, Shimorin showed that a certain factorization condition on $(…