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TRACES ARISING FROM REGULAR INCLUSIONS

Part of: Selfadjoint operator algebras

Published online by Cambridge University Press:  03 November 2016

DANNY CRYTSER  and
GABRIEL NAGY
DANNY CRYTSER*
Affiliation:
Department of Mathematics, Kansas State University, Manhattan, KS 66503, USA email [email protected]
GABRIEL NAGY
Affiliation:
Department of Mathematics, Kansas State University, Manhattan, KS 66503, USA email [email protected]
*
✉[email protected]
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Abstract

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We study the problem of extending a state on an abelian $C^{\ast }$-subalgebra to a tracial state on the ambient $C^{\ast }$-algebra. We propose an approach that is well suited to the case of regular inclusions, in which there is a large supply of normalizers of the subalgebra. Conditional expectations onto the subalgebra give natural extensions of a state to the ambient $C^{\ast }$-algebra; we prove that these extensions are tracial states if and only if certain invariance properties of both the state and conditional expectations are satisfied. In the example of a groupoid $C^{\ast }$-algebra, these invariance properties correspond to invariance of associated measures on the unit space under the action of bisections. Using our framework, we are able to completely describe the tracial state space of a Cuntz–Krieger graph algebra. Along the way we introduce certain operations called graph tightenings, which both streamline our description and provide connections to related finiteness questions in graph $C^{\ast }$-algebras. Our investigation has close connections with the so-called unique state extension property and its variants.

Keywords

operator algebrastracial statesC∗ -algebrasgraph algebras

MSC classification

Primary: 46L30: States
Type
Research Article
Information
Journal of the Australian Mathematical Society , Volume 103 , Issue 2 , October 2017 , pp. 190 - 230
Copyright
© 2016 Australian Mathematical Publishing Association Inc. 

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