On Kapranov's description of M0,n as a Chow quotient

Abstract

We provide a direct proof, valid in arbitrary characteristic, of the result originally proven by Kapranov over C that the Hilbert quotient (P 1 ) n //H PGL2 and Chow quotient (P 1 ) n //Ch PGL2 are isomorphic to M0,n . In both cases this is done by explicitly constructing the universal family of orbit closures and then showing that the induced morphism is an isomorphism onto its image. The proofs of these results in many ways reduce to the case n = 4; in an appendix we outline a formalism of this phenomenon relating to certain operads.