Coble type hypersurfaces and hyperkähler fourfolds

Abstract

A classical result, already observed by Coble, asserts that a genus 2 Jacobian can be embedded in ${\mathbf{P}}^8$ as the singular locus of a unique cubic hypersurface; similarly, the Kummer of a genus 3 Jacobian is embedded in ${\mathbf{P}}^7$ as the singular locus of a unique quartic hypersurface. We present a precise analogue of these results in the context of hyperkähler fourfolds: for the general member in the 20-dimensional locally complete families of polarized hyperkähler fourfolds of ${K3}^{[2]}$-type with squares 4 or 6 and divisibility 1, we establish the existence of a unique Coble type hypersurface. As a consequence, we describe several geometric aspects of the corresponding moduli spaces.

33 pages