Complete symplectic quadrics and Kontsevich spaces of conics in Lagrangian Grassmannians

Abstract

A wonderful compactification of an orbit under the action of a semi-simple and simply connected group is a smooth projective variety containing the orbit as a dense open subset, and where the added boundary divisor is simple normal crossing. We construct the wonderful compactification of the space of symmetric and symplectic matrices, and investigate its geometry. As an application, we describe the birational geometry of the Kontsevich spaces parametrizing conics in Lagrangian Grassmannians. Contents 1. Introduction 1 2. Complete quadrics 4 3. Complete symmetric symplectic forms 8 4. Divisors on S 2r 14 5. Birational geometry of S 2r 17 6. Moduli spaces of conics in Lagrangian Grassmannians 20 References 28