A Computation with the Connes–Thom Isomorphism

Sundar, S.

Canadian mathematical bulletin, Tome 58 (2015) no. 4, pp. 846-857

Résumé

Let $A\,\in \,{{M}_{n}}\left( \mathbb{R} \right)$ be an invertible matrix. Consider the semi-direct product ${{\mathbb{R}}^{n}}\rtimes \,\mathbb{Z}$ where the action of $\mathbb{Z}$ on ${{\mathbb{R}}^{n}}$ is induced by the left multiplication by $A$ . Let $\left( \alpha ,\,\tau\right)$ be a strongly continuous action of ${{\mathbb{R}}^{n}}\rtimes \,\mathbb{Z}$ on a ${{C}^{*}}$ -algebra $B$ where $\alpha$ is a strongly continuous action of ${{\mathbb{R}}^{n}}$ and $\tau$ is an automorphism. The map $\tau$ induces a map $\widetilde{\tau }\,\text{on}\,\text{B}\,{{\rtimes }_{\alpha }}\,{{\mathbb{R}}^{n}}$ . We show that, at the $K$ -theory level, $\tau$ commutes with the Connes–Thom map if $\det \left( A \right)\,>\,0$ and anticommutes if $\det \left( A \right)\,>\,0$ . As an application, we recompute the $K$ -groups of the Cuntz–Li algebra associated with an integer dilation matrix.

Détail

DOI : 10.4153/CMB-2015-048-6

Mots-clés : 46L80, 58B34, K-theory, Connes–Thom isomorphism, Cuntz–Li algebras