Varieties for Modules of Quantum Elementary Abelian Groups

Abstract

We define a rank variety for a module of a noncocommutative Hopf algebra $A = Λ\rtimes G$ where $Λ= k[X_1, ..., X_m]/(X_1^{\ell}, ..., X_m^{\ell})$, $G = ({\mathbb Z}/\ell{\mathbb Z})^m$, and $\text{char} k$ does not divide $\ell$, in terms of certain subalgebras of $A$ playing the role of "cyclic shifted subgroups". We show that the rank variety of a finitely generated module $M$ is homeomorphic to the support variety of $M$ defined in terms of the action of the cohomology algebra of $A$. As an application we derive a theory of rank varieties for the algebra $Λ$. When $\ell=2$, rank varieties for $Λ$-modules were constructed by Erdmann and Holloway using the representation theory of the Clifford algebra. We show that the rank varieties we obtain for $Λ$-modules coincide with those of Erdmann and Holloway.