Compatible Decomposition of the Casselman Algebra and the Reduced Group C*-algebra of a Real Reductive Group

Abstract

For a real reductive group $G$, we investigate the structure of the Casselman algebra $\mathcal{S}(G)$ and its similarities to the structure of the reduced group $C^*$-algebra $C_r^*(G)$. We demonstrate that the two algebras are assembled from very similar elementary components in a compatible way. In particular, we prove that the two algebras have the same $K$-theory when restricted to a finite set of $K$-types, which is a refinement of the Connes-Kasparov isomorphism.