Homotopy type of the unitary group of the uniform Roe algebra on $\mathbb{Z}^n$

Abstract

We study the homotopy type of the space of the unitary group $\U_1(C^\ast_u(|\mathbb{Z}^n|))$ of the uniform Roe algebra $C^\ast_u(|\mathbb{Z}^n|)$ of $\mathbb{Z}^n$. We show that the stabilizing map $\U_1(C^\ast_u(|\mathbb{Z}^n|))\to\U_\infty(C^\ast_u(|\mathbb{Z}^n|))$ is a homotopy equivalence. Moreover, when $n=1,2$, we determine the homotopy type of $\U_1(C^\ast_u(|\mathbb{Z}^n|))$, which is the product of the unitary group $\U_1(C^\ast(|\mathbb{Z}^n|))$ (having the homotopy type of $\U_\infty(\mathbb{C})$ or $\mathbb{Z}\times B\U_\infty(\mathbb{C})$ depending on the parity of $n$) of the Roe algebra $C^\ast(|\mathbb{Z}^n|)$ and rational Eilenberg--MacLane spaces.