The Partial-Isometric Crossed Products by Semigroups of Endomorphisms as Full Corners

Abstract

Suppose $\Gamma^{+}$ is the positive cone of a totally ordered abelian group $\Gamma$, and $(A,\Gamma^{+},\alpha)$ is a system consisting of a $C^*$-algebra $A$, an action $\alpha$ of $\Gamma^{+}$ by extendible endomorphisms of $A$. We prove that the partial-isometric crossed product $A\times_{\alpha}^{\piso}\Gamma^{+}$ is a full corner in the subalgebra of $\L(\ell^{2}(\Gamma^{+},A))$, and that if $\alpha$ is an action by automorphisms of $A$, then it is the isometric-crossed product $(B_{\Gamma^{+}}\otimes A)\times^{\iso}\Gamma^{+}$, which is therefore a full corner in the usual crossed product of system by a group of automorphisms. We use these realizations to identify the ideal of $A\times_{\alpha}^{\piso}\Gamma^{+}$ such that the quotient is the isometric crossed product $A\times_{\alpha}^{\iso}\Gamma^{+}$.