Toric polar maps and characteristic classes

Abstract

Given a hypersurface in the complex projective space, we prove that the degree of its toric polar map is given by the signed topological Euler characteristic of a distinguished open set, namely the complement of the union of the hypersurface and the coordinate hyperplanes. In addition, we prove that if the hypersurface is in general position or is nondegenerate with respect to its Newton polytope, then the coefficients of the Chern-Schwartz-MacPherson class of the distinguished open set agree, up to sign, with the multidegrees of the toric polar map. In the latter case, we also recover the multidegrees from mixed volumes.For plane curves, a precise formula for the degree of the toric polar map is obtained in terms of local invariants. Finally, we construct families, in arbitrary dimension, of irreducible hypersurfaces whose toric polar map is birational.