Generalized partial-estimate conjecture for operator-valued inner functions

From papers

Let EE be a closed subset of the unit circle T\mathbb{T} such that E=0|E|=0. Let F\mathcal{F} and F\mathcal{F}' be separable Hilbert spaces, and let Θ:(CE)L(F,F)\Theta:(\mathbb{C}_\infty\setminus E)\to\mathcal{L}(\mathcal{F},\mathcal{F}') be a holomorphic function whose restriction to the unit disk is an inner function, with Θ(λ)\Theta(\lambda) purely contractive for every λD\lambda\in\mathbb{D}. Generalized partial-estimate conjecture. There exists a positive sequence ϵn0\epsilon_n\to0 such that

lim infnδn(Θ)ϵn=0.\liminf_{n\to\infty}\frac{\delta_n(\Theta)}{\epsilon_n}=0.

Here δn(Θ)\delta_n(\Theta) is the quantity defined in the paper's partial-estimate theorem. This conjecture would remove the finite-rank hypothesis from the main theorem and thereby imply Esterle's Hilbert-space contraction conjecture. The paper does not establish it in the general operator-valued setting.

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Sources & referencesView supporting material

Primary source

Thomas Ransford, “Negative powers of Hilbert-space contractions”, arXiv:2310.10754 (2024).

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