Automorphism Groups of Deformations and Quantizations of Kleinian Singularities

It is known that, for the algebra of functions on a Kleinian singularity, the parameter space of deformations and the parameter space of quantizations coincide. We prove that, for a Kleinian singularity of type $A$ or $D$ , isomorphisms between the quantizations are essentially the same as Poisson isomorphisms between deformations. In particular, the group of automorphisms of the deformation and the quantization corresponding to the same deformation parameter are isomorphic. We additionally describe the groups of automorphisms as abstract groups: for type $A$ they have an amalgamated free product structure, for type $D$ they are subgroups of the groups of Dynkin diagram automorphisms. For type $D$ we also compute all the possible affine isomorphisms between deformations; this was not known before.