Combinatorial simpliciality of arrangements of hyperplanes

Abstract

We introduce a combinatorial characterization of simpliciality for arrangements of hyperplanes. We then give a sharp upper bound for the number of hyperplanes of such an arrangement in the projective plane over a finite field, and present some series of arrangements related to the known arrangements in characteristic zero. We further enumerate simplicial arrangements with given symmetry groups. Finally, we determine all finite complex reflection groups affording combinatorially simplicial arrangements. It turns out that combinatorial simpliciality coincides with inductive freeness for finite complex reflection groups except for the Shephard-Todd group $G_{31}$.

19 pages. This version contains a definition of simpliciality for arbitrary dimensions as suggested by M. Falk; moreover, the section on reflection arrangements is now extended to arbitrary finite irreducible complex reflection groups