Model theory of Hilbert spaces expanded by normal operators

Alexander Berenstein; Nicolás Cuervo Ovalle; Isaac Goldbring

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arXiv · 2507.21894

Model theory of Hilbert spaces expanded by normal operators

Alexander Berenstein·Nicolás Cuervo Ovalle·Isaac Goldbring

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Abstract

We study expansions of Hilbert spaces with a bounded normal operator $T$. We axiomatize this theory in a natural language and identify all of its completions. We prove the definability of the adjoint $T^*$ and prove quantifier elimination for every completion after adding $T^*$ to the language. We identify types with measures on the spectrum of the operator and show that the logic topology on the type space corresponds to the weak*-topology on the space of measures. We also give a precise formula for the metric on the space of $1$-types. We prove all completions are stable and characterize the stability spectrum of the theory in terms of the spectrum of the operator. We also show all completions, regardless of their spectrum, are $\omega$-stable up to perturbations.

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BibTeX RIS

Alexander Berenstein, Nicolás Cuervo Ovalle, Isaac Goldbring. 2025-07-29. Model theory of Hilbert spaces expanded by normal operators. https://arxiv.org/abs/2507.21894

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