(Quantum) discreteness, spectrum compactness and uniform continuity

We prove a number of results linking properties of actions by compact groups (both quantum and classical) on Banach spaces, such as uniform continuity, spectrum finiteness and extensibility of the actions across several constructions. Examples include: (a) a unitary representation of a compact quantum group induces a continuous action on the C^{*} -algebra of bounded operators if and only if it has finitely many isotypic components, and hence is uniformly continuous; (b) a compact quantum group is finite if and only if its continuous actions on C^{*} -algebras lift to continuous actions on either the multiplier algebras or von Neumann envelopes thereof; (c) a (classical) locally compact group \mathbb{G} is discrete if and only if the forgetful functor from \mathbb{G} -acted-upon compact T_{2} spaces back to compact T_{2} spaces creates coproducts; (d) a representation of a linearly reductive quantum group has finitely many isotypic components if and only if its restrictions to two topologically-generating quantum subgroups, one of which is normal, do; (e) equivalent characterizations of uniform continuity for actions of compact groups on Banach spaces, e.g., that such an action is uniformly continuous if and only if its restrictions to a pro-torus and to pro- p subgroups are.

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Publication Details

Journal
Journal of Noncommutative Geometry
Published
2025-01-09
DOI
https://doi.org/10.4171/jncg/604
Citations
2
Primary Topic
Quantum Mechanics and Applications
Type
article
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article

(Quantum) discreteness, spectrum compactness and uniform continuity

Alexandru Chirvăsitu
2 citations
Journal of Noncommutative Geometry
Quantum Mechanics and Applications
article

(Quantum) discreteness, spectrum compactness and uniform continuity

Alexandru Chirvăsitu
article en
2 citations

Abstract

We prove a number of results linking properties of actions by compact groups (both quantum and classical) on Banach spaces, such as uniform continuity, spectrum finiteness and extensibility of the actions across several constructions. Examples include: (a) a unitary representation of a compact quantum group induces a continuous action on the C^{*} -algebra of bounded operators if and only if it has finitely many isotypic components, and hence is uniformly continuous; (b) a compact quantum group is finite if and only if its continuous actions on C^{*} -algebras lift to continuous actions on either the multiplier algebras or von Neumann envelopes thereof; (c) a (classical) locally compact group \mathbb{G} is discrete if and only if the forgetful functor from \mathbb{G} -acted-upon compact T_{2} spaces back to compact T_{2} spaces creates coproducts; (d) a representation of a linearly reductive quantum group has finitely many isotypic components if and only if its restrictions to two topologically-generating quantum subgroups, one of which is normal, do; (e) equivalent characterizations of uniform continuity for actions of compact groups on Banach spaces, e.g., that such an action is uniformly continuous if and only if its restrictions to a pro-torus and to pro- p subgroups are.

Journal of Noncommutative GeometryVol. 20(1)
University at Buffalo, State University of New York (US)
Openalex Percentile: Top 99%
Quantum Mechanics and Applications
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(Quantum) discreteness, spectrum compactness and uniform continuity — Alexandru Chirvăsitu · Journal of Noncommutative Geometry (2025) | TGRS Research Map | TGRS