Determinantal varieties from point configurations on hypersurfaces

Abstract

We consider the scheme $X_{r,d,n}$ parametrizing $n$ ordered points in projective space ${\mathbb{P}}^r$ that lie on a common hypersurface of degree $d$. We show that this scheme has a determinantal structure and we prove that it is irreducible, Cohen-Macaulay, and normal. Moreover, we give an algebraic and geometric description of the singular locus of $X_{r,d,n}$ in terms of Castelnuovo-Mumford regularity and $d$-normality. This yields a characterization of the singular locus of $X_{2,d,n}$ and $X_{3,2,n}$.

24 pages. Final version with minor corrections. To appear in International Mathematics Research Notices