Self-duality of Coble's quartic hypersurface and applications

Abstract

The moduli space M_0 of semi-stable rank 2 vector bundles with fixed trivial determinant over a non-hyperelliptic curve C of genus 3 is isomorphic to a quartic hypersurface in P^7 (Coble's quartic). We show that M_0 is self-dual and that its polar map associates to a stable bundle E \in M_0 a bundle F which is characterized by dim H^0(C, E \otimes F) = 4. The projective space PH^0(C, E \otimes F) is equipped with a net of quadrics Πand it is shown that the map which associates to E \in M_0 the isomorphism class of the plane quartic Hessian curve of Πis a dominant map to the moduli space of genus 3 curves.