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arXiv · 2509.19792

Numerical Ranges and Spectral Sets: the unbounded case

Michel Crouzeix
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Abstract

It is known that, if $\Omega$ $\subset$ C is a convex set containing the numerical range of an operator A, then $\Omega$ is a C $\Omega$ -spectral set for A with C $\Omega$ $\le$ 1+ $\sqrt$ 2. We improve this estimate in unbounded cases.

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Michel Crouzeix. 2025-09-24. Numerical Ranges and Spectral Sets: the unbounded case. https://arxiv.org/abs/2509.19792

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