The injective envelope of simple modules over Leavitt path algebras II: simples arising from exclusive cycles

Abstract: Let $K$ be any field, $E$ any directed graph, and $L_K(E)$ the associated Leavitt path algebra. As described first by Chen, and subsequently generalized by Ara and Rangaswamy, for each cycle $c$ in $E$ one can build the simple left $L_K(E)$-module $V_c<sup>E$, and then more generally $V_{p(x),c}<sup>E$ (where $p(x)$ is an irreducible polynomial in $K[x,x<sup>{-1}]$). A cycle $c$ is called {\it exclusive} in case none of the vertices of $c$ is the base of any cycle other than $c$. In our main result we provide an explicit description of the injective envelope of $V_c<sup>E$, and then more generally of $V_{p(x),c}<sup>E$, for each exclusive cycle $c$. Our method involves defining an $L_K(E)$-module structure on an appropriately-built $K$-vector space of infinite series. Our main result significantly generalizes previous work of the authors, in that the result holds for all graphs (finite or not), and all exclusive cycles.