On Z-graded associative algebras and their N-graded modules

Abstract

Let $A$ be a $Z$-graded associative algebra and let $\rho$ be an irreducible $N$-graded representation of $A$ on $W$ with finite-dimensional homogeneous subspaces. Then it is proved that $\rho(\tilde{A})=gl_{J}(W)$, where $\tilde{A}$ is the completion of $A$ with respect to a certain topology and $gl_{J}(W)$ is the subalgebra of $\End W$, generated by homogeneous endomorphisms. It is also proved that an $N$-graded vector space $W$ with finite-dimensional homogeneous spaces is the only continuous irreducible $N$-graded $gl_{J}(W)$-module up to equivalence, where $gl_{J}(W)$ is considered as a topological algebra in a certain natural way, and that any continuous $N$-graded $gl_{J}(W)$-module is a direct sum of some copies of $W$. A duality for certain subalgebras of $gl_{J}(W)$ is also obtained.