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5. Functional Analysis, Operator Theory and Operator Algebras, Mathematical Physics

$C^*$-algebras from $k$ group representations

Valentin Deaconu
University of Nevada, Reno, USA

Abstract:

We introduce certain $C^*$-algebras and $k$-graphs associated to $k$ finite dimensional unitary representations $\rho_1,...,\rho_k$ of a compact group $G$. We define a higher rank Doplicher-Roberts algebra $\mathcal O_{\rho_1,...,\rho_k}$, constructed from intertwiners of tensor powers of these representations. Under certain conditions, we show that this $C^*$-algebra is isomorphic to a corner in the $C^*$-algebra of a row finite rank $k$ graph $\Lambda$ with no sources. For $G$ finite and $\rho_i$ faithful of dimension at least $2$, this graph is irreducible, it has vertices $\hat{G}$ and the edges are determined by $k$ commuting matrices obtained from the character table of the group. We illustrate with some examples when $\mathcal O_{\rho_1,...,\rho_k}$ is simple and purely infinite, and with some $K$-theory computations.