Varieties for Modules of Quantum Elementary Abelian Groups

We define a rank variety for a module of a noncocommutative Hopf algebra $A = \Lambda \rtimes G$where$\Lambda = k[X_1, …, X_m]/(X_1^{\ell}, …, X_m^{\ell})$,$G = ({\mathbb Z}/\ell{\mathbb Z})^m$,and$$\text{char}$ k$ does not divide $\mathrm{\ell }$, 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 $\mathrm{\Lambda }$. When $\mathrm{\ell }=2$, rank varieties for $\mathrm{\Lambda }$-modules were constructed by Erdmann and Holloway using the representation theory of the Clifford algebra. We show that the rank varieties we obtain for $\mathrm{\Lambda }$-modules coincide with those of Erdmann and Holloway.