Triangular arrangements on the projective plane

Abstract

In this work we study line arrangements consisting in lines passing through three non-aligned points. We call them triangular arrangements. We prove that any combinatorics of a triangular arrangement is always realized by a Roots-of-Unity-Arrangement, which is a particular class of triangular arrangements. Among these Roots-of Unity-Arrangements, we provide conditions that ensure their freeness. Finally, we give two triangular arrangements having the same weak combinatorics, such that one is free but the other one is not.

Keywords

• mathematics - algebraic geometry
• mathematics - algebraic topology
• mathematics - combinatorics
• 52c35, 14f06, 32s22