Compact anti-self-dual orbifolds with torus actions

Abstract

We give a classification of toric anti-self-dual conformal structures on compact 4-orbifolds with positive Euler characteristic. Our proof is twistor theoretic: the interaction between the complex torus orbits in the twistor space and the twistor lines induces meromorphic data, which we use to recover the conformal structure. A compact anti-self-dual orbifold can also be constructed by adding a point at infinity to an asymptotically locally Euclidean (ALE) scalar-flat K\"ahler orbifold. We use this observation to classify ALE scalar-flat K\"ahler 4-orbifolds whose isometry group contain a 2-torus.