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Cartan subalgebras of regular extensions of von Neumann algebras

Part of: Selfadjoint operator algebras Locally compact groups and their algebras

Published online by Cambridge University Press:  09 April 2009

Colin E. Sutherland
Colin E. Sutherland
Affiliation:
Mathematics Department The University of New South WalesP.O. Box 1 Kensington, N.S.W. 2033, Australia
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Abstract

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We analyse the structure of a regular extension ℳ ⋊ γ, υQ of a von Neumann algebra ℳ by an action (modulo inner automorphisms) γ of a discrete group Q, and a nonabelian 2-cycle υ for γ, under the assumption that the “action” γ of Q is cocycle conjugate to an “action”, α which leaves globally invariant a cartan subalgebra of ℳ. we show that ℳ ⋊ γ, υQ is isomorphic with the algebra of the left regular projective representation of a certain discrete, non-principal groupoid ℜ V Q determined by the action of Q on the given cartan subalgebrs, where ℜ is the Takesaki relation associated to the pair (ℳ, ) we apply this description to give a decomposition of the regular representation of a group G into irreducibles, where G is a split extension of a type I group K by an abelian group Q, and work out the details of the author's earlier abstract plancherel theorem in the case when K is abelian.

MSC classification

Secondary: 46L10: General theory of von Neumann algebras 22D25: $C^*$-algebras and $W^*$-algebras in relation to group representations
Type
Research Article
Information
Journal of the Australian Mathematical Society , Volume 45 , Issue 2 , October 1988 , pp. 249 - 274
Copyright
Copyright © Australian Mathematical Society 1988

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