A characterization of the Razak–Jacelon algebra

Abstract

Combing Elliott, Gong, Lin and Niu's result and Castillejos and Evington's result, we see that if $A$ is a simple separable nuclear monotracial C$^*$-algebra, then $A\otimes\mathcal{W}$ is isomorphic to $\mathcal{W}$ where $\mathcal{W}$ is the Razak-Jacelon algebra. In this paper, we give another proof of this. In particular, we show that if $\mathcal{D}$ is a simple separable nuclear monotracial $M_{2^{\infty}}$-stable C$^*$-algebra which is $KK$-equivalent to $\{0\}$, then $\mathcal{D}$ is isomorphic to $\mathcal{W}$ without considering tracial approximations of C$^*$-algebras with finite nuclear dimension. Our proof is based on Matui and Sato's technique, Schafhauser's idea in his proof of the Tikuisis-White-Winter theorem and properties of Kirchberg's central sequence C$^*$-algebra $F(\mathcal{D})$ of $\mathcal{D}$. Note that some results for $F(\mathcal{D})$ is based on Elliott-Gong-Lin-Niu's stable uniqueness theorem. Also, we characterize $\mathcal{W}$ by using properties of $F(\mathcal{W})$. Indeed, we show that a simple separable nuclear monotracial C$^*$-algebra $D$ is isomorphic to $\mathcal{W}$ if and only if $D$ satisfies the following properties:(i) for any $\theta\in [0,1]$, there exists a projection $p$ in $F(D)$ such that $\tau_{D, \omega}(p)=\theta$,(ii) if $p$ and $q$ are projections in $F(D)$ such that $0<\tau_{D, \omega}(p)=\tau_{D, \omega}(q)$, then $p$ is Murray-von Neumann equivalent to $q$,(iii) there exists a homomorphism from $D$ to $\mathcal{W}$.