On the numerical Terao's conjecture and Ziegler pairs for line arrangements

Abstract

In this paper we present a smallest possible counterexample to the Numerical Terao's Conjecture in the class of line arrangements in the complex projective plane. Our example consists of a pair of two arrangements with $13$ lines. Moreover, we use the newly discovered singular matroid realization spaces to construct new examples of pairs of line arrangements having the same underlying matroid but different free resolutions of the Milnor algebras. Such rare arrangements are called Ziegler pairs in the literature.

14 pages, is the final version, incorporating the referee's comments, to appear in the Journal of Commutative Algebra