The boundary manifold of a complex line arrangement

We study the topology of the boundary manifold of a line arrangement in CP , with emphasis on the fundamental group G and associated invariants. We determine the Alexander polynomial ∆(G), and more generally, the twisted Alexander polynomial associated to the abelianization of G and an arbitrary complex representation. We give an explicit description of the unit ball in the Alexander norm, and use it to analyze certain Bieri–Neumann–Strebel invariants of G . From the Alexander polynomial, we also obtain a complete description of the first characteristic variety of G . Comparing this with the corresponding resonance variety of the cohomology ring of G enables us to characterize those arrangements for which the boundary manifold is formal.