Equivariant Elliptic Cohomology and Mapping Stacks

We introduce a new cohomology theory for stacks called elliptic Hochschild homology, prove some fundamental properties and compute it in some classes of examples. We then introduce its periodic cyclic version and show that, over the complex numbers and for a quotient stack, this recovers Grojnowski’s equivariant elliptic cohomology of the analytification.