Conformal blocks and rational normal curves

Abstract

We prove that the Chow quotient parametrizing configurations of n points in ${\mathbb{P}}^d$ which generically lie on a rational normal curve is isomorphic to ${\overline{M}}_{0,n}$, generalizing the well-known $d=1$ result of Kapranov. In particular, ${\overline{M}}_{0,n}$ admits birational morphisms to all the corresponding geometric invariant theory (GIT) quotients. For symmetric linearizations the polarization on each GIT quotient pulls back to a divisor that spans the same extremal ray in the symmetric nef cone of ${\overline{M}}_{0,n}$ as a conformal blocks line bundle. A symmetry in conformal blocks implies a duality of point-configurations that comes from Gale duality and generalizes a result of Goppa in algebraic coding theory. In a suitable sense, ${\overline{M}}_{0,2m}$ is fixed pointwise by the Gale transform when $d=m-1$ so stable curves correspond to self-associated configurations.

17 pages, 1 figure; published version