Book contents
- Frontmatter
- Contents
- Contributors
- Preface
- 1 Left Relatively Convex Subgroups
- 2 Groups with Context-free Co-word Problem and Embeddings into Thompson’s Group V
- 3 Limit Sets for Modules over Groups Acting on a CAT(0) Space
- 4 Ideal Structure of the C∗-algebra of R. Thompson’s group T
- 5 Local Similarity Groups with Context-free Co-word Problem
- 6 Compacta with Shapes of Finite Complexes: a Direct Approach to the Edwards–Geoghegan–Wall
- 7 The Horofunction Boundary of the Lamplighter Group L2 with the Diestel–Leader metric
- 8 Intrinsic Geometry of a Euclidean Simplex
- 9 Hyperbolic Dimension and Decomposition Complexity
- 10 Some Remarks on the Covering Groups of a Topological Group
- 11 The Σ-invariants of Thompson’s group F via Morse Theory
4 - Ideal Structure of the C∗-algebra of R. Thompson’s group T
Published online by Cambridge University Press: 27 August 2018
- Frontmatter
- Contents
- Contributors
- Preface
- 1 Left Relatively Convex Subgroups
- 2 Groups with Context-free Co-word Problem and Embeddings into Thompson’s Group V
- 3 Limit Sets for Modules over Groups Acting on a CAT(0) Space
- 4 Ideal Structure of the C∗-algebra of R. Thompson’s group T
- 5 Local Similarity Groups with Context-free Co-word Problem
- 6 Compacta with Shapes of Finite Complexes: a Direct Approach to the Edwards–Geoghegan–Wall
- 7 The Horofunction Boundary of the Lamplighter Group L2 with the Diestel–Leader metric
- 8 Intrinsic Geometry of a Euclidean Simplex
- 9 Hyperbolic Dimension and Decomposition Complexity
- 10 Some Remarks on the Covering Groups of a Topological Group
- 11 The Σ-invariants of Thompson’s group F via Morse Theory
Summary
We explore the ideal structure of the reduced C∗-algebra of R. Thompson’s group T. We show that even though T has trace, one cannot use the Kesten Condition to verify that the reduced C∗-algebra of T is simple. At the time of the initial writing of this chapter, there had been no example group for which it was known that the Kesten Condition would fail to prove simplicity, even though the group has trace. Motivated by this first result, we describe a class of groups where even if the group has trace, one cannot apply the Kesten Condition to verify the simplicity of those groups' reduced C∗-algebras. We also offer an apparently weaker condition to test for the simplicity of a group's reduced C∗-algebra, and we show this new test is still insufficient to show that the reduced C∗-algebra of T is simple. Separately, we find a controlled version of a Ping-Pong Lemma which allows one to find non-abelian free subgroups in groups of homeomorphisms of the circle generated by elements with rational rotation number. We use our Ping-Pong Lemma to find a simple converse to a theorem of Uffe Haagerup and Kristian Knudsen Olesen.
- Type
- Chapter
- Information
- Topological Methods in Group Theory , pp. 46 - 66Publisher: Cambridge University PressPrint publication year: 2018