Internal Zonotopal Algebras and the Monomial Reflection Groups

Abstract: The group $G(m,1,n)$ consists of $n$-by-$n$ monomial matrices whose entries are $m$th roots of unity. It is generated by $n$ complex reflections acting on $\mathbf{C}^n$. The reflecting hyperplanes give rise to a (hyperplane) arrangement $\mathcal{G} \subset \mathbf{C}^n$. The internal zonotopal algebra of an arrangement is a finite dimensional algebra first studied by Holtz and Ron. Its dimension is the number of bases of the associated matroid with zero internal activity. In this paper we study the structure of the internal zonotopal algebra of the Gale dual of the reflection arrangement of $G(m,1,n)$, as a representation of this group. Our main result is a formula for the top degree component as an induced character from the cyclic group generated by a Coxeter element. We also provide results on representation stability, a connection to the Whitehouse representation in type~A, and an analog of decreasing trees in type~B.