Formal Verlinde Module

Abstract: Let G be a compact, simple and simply connected Lie group and $\A$ be an equivariant Dixmier-Douady bundle over G. For any fixed level k, we can define a G-C*-algebra $C_{\A^{k+h}}(G)$ as all the continuous sections of the tensor power $\A^{k+h}$ vanishing at infinity. A deep theorem by Freed-Hopkins-Teleman showed that the twisted K-homology $KK^{G}(C_{\A^{k+h}}(G), \C)$ is isomorphic to the level k Verlinde ring R_{k}(G). By the construction of crossed product, we define a C*-algebra $C^{*}(G,C_{\A^{k+h}}(G))$. We show that the K-homology KK(C^{*}(G,C_{\A^{k+h}}(G)),\C) is isomorphic to the formal Verlinde module $R^{-\infty}(G) \otimes_{R(G)} R_{k}(G)$, where $R^{-\infty}(G) = Hom_{\Z}(R(G),\Z)$ is the completion of the representation ring.