Crepant resolutions of weighted projective spaces and quantum deformations

Abstract

We compare the Chen-Ruan cohomology ring of the weighted projective spaces $\IP(1,3,4,4)$ and $\IP(1,...,1,n)$ with the cohomology ring of their crepant resolutions. In both cases, we prove that the Chen-Ruan cohomology ring is isomorphic to the quantum corrected cohomology ring of the crepant resolution after suitable evaluation of the quantum parameters. For this, we prove a formula for the Gromov-Witten invariants of the resolution of a transversal ${\rm A}_3$ singularity.

Exposition improved, new title, typos corrected. The section concerning the model for the orbifold Chow ring has been removed (appears now in our new preprint 0709.4559)