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A C*-algebraic Schoenberg theorem
Journal article   Open access

A C*-algebraic Schoenberg theorem

Ola Bratteli, Palle E. T. Jorgensen, Akitaka Kishimoto and Donald W. Robinson
Annales de l'Institut Fourier, Vol.34(3), pp.155-187
1984
DOI: 10.5802/aif.981
url
https://doi.org/10.5802/aif.981View
Published (Version of record) Open Access

Abstract

Let 𝔄 be a �*-algebra, � a compact abelian group, � an action of � by *-automorphisms of 𝔄,𝔄� the fixed point algebra of � and 𝔄� the dense sub-algebra of �-finite elements in 𝔄. Further let � be a linear operator from 𝔄� into 𝔄 which commutes with � and vanishes on 𝔄�. We prove that � is a complete dissipation if and only if � is closable and its closure generates a �0-semigroup of completely positive contractions. These complete dissipations are classified in terms of certain twisted negative definite maps from the dual group �^ into dissipative operators affiliated with the center of the multiplier algebra of 𝔄�. We also argue that the complete dissipation property is strictly stronger than the usual dissipation property, except in special circumstances such as when 𝔄 is abelian.

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