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arXiv · 1609.08837

Bass--Serre trees of amalgamated free product C*-algebras

Kei Hasegawa
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Abstract

For any reduced amalgamated free product $\mathrm{C}^*$-algebra $(A,E)=(A_1, E_1) \ast_D (A_2,E_2)$, we introduce and study a canonical ambient $\mathrm{C}^*$-algebra $Δ\mathbf{T}(A,E)$ of $A$ which generalizes the crossed product arising from the canonical action of an amalgamated free product group on the compactification of the associated Bass--Serre tree. Using an explicit identification of $Δ\mathbf{T}(A,E)$ with a Cuntz--Pimsner algebra we prove two kinds of "amenability" results for $Δ\mathbf{T}(A,E)$; nuclearity and universality. As applications of our framework, we provide new conceptual, and simpler proofs of several known theorems on approximation properties, embeddability, and $KK$-theory for reduced amalgamated free product $\mathrm{C}^*$-algebras.

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Kei Hasegawa. 2017-02-21. Bass--Serre trees of amalgamated free product C*-algebras. https://arxiv.org/abs/1609.08837

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