An index theorem on anti-self-dual orbifolds

An index theorem for the anti-self-dual deformation complex on anti-self-dual orbifolds with singularities conjugate to ADE-type is proved. In 1988, Claude Lebrun gave examples of scalar-flat K\"ahler ALE metrics with negative mass, on the total space of the bundle $\mathcal{O}(-n)$ over $S^2$. A corollary of this index theorem is that the moduli space of anti-self-dual ALE metrics near each of these metrics has dimension at least $4n-12$, and thus for $n \geq 4$ the LeBrun metrics admit a plethora of non-trivial anti-self-dual deformations.