On the uniqueness of Kerr-de Sitter spacetimes

In this paper, we prove a series of results concerning the uniqueness of Kerr-de Sitter as a family of smooth stationary black hole solutions to the nonlinear Einstein vacuum equations with positive cosmological constant $Λ$. The results only assume smoothness rather than analyticity of the solution in question. The results use a two-sided approach to rigidity, requiring assumptions on both the event horizon and the cosmological horizon (or a neighborhood thereof) to formulate an appropriate unique continuation argument to prove the rigidity of Kerr-de Sitter.