The Picard groups of inclusions of $C^{\ast }$-algebras induced by equivalence bimodules

Abstract

Let $A$ and $B$ be $\sigma$-unital $C^{\ast }$-algebras and $X$ and $Y$ an $A-A$-equivalence bimodule and a $B-B$-equivalence bimodule, respectively. Also, let $A{⋊}_X\mathbb{Z}$ and $B{⋊}_Y\mathbb{Z}$ be the crossed products of $A$ and $B$ by $X$ and $Y$, respectively. Furthermore, let $A\subset A{⋊}_X\mathbb{Z}$ and $B\subset B{⋊}_Y\mathbb{Z}$ be the inclusions of $C^{\ast }$-algebras induced by $X$ and $Y$, respectively. We suppose that $A^{\prime }\cap M(A{⋊}_X\mathbb{Z})=\mathbb{C}1$. In this paper we shall show that the inclusions $A\subset A{⋊}_X\mathbb{Z}$ and $B\subset B{⋊}_Y\mathbb{Z}$ are strongly Morita equivalent if and only if there is an $A-B$-equivalence bimodule $M$ such that $Y\cong \tilde{M}{\otimes }_{A}X{\otimes }_{A}M$ or $\tilde{Y}\cong \tilde{M}{\otimes }_{A}X{\otimes }_{A}M$ as $B-B$-equivalence bimodules, where $\tilde{M}$ and $\tilde{Y}$ are the dual $B-A$-equivalence bimodule and the dual $B-B$-equivalence bimodule of $M$ and $Y$, respectively. Applying this result, we shall compute the Picard group of the inclusion $A\subset A{⋊}_X\mathbb{Z}$ under the assumption that $A^{\prime }\cap M(A{⋊}_X\mathbb{Z})=\mathbb{C}1$.

12 pages

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