Black-Hole No-Hair Theorems for a Positive Cosmological Constant

We extend all known black-hole no-hair theorems to space-times endowed with a positive cosmological constant $\Lambda$. Specifically, we prove that static spherical black holes with $\Lambda >0$ cannot support scalar fields in convex potentials and Proca-massive vector fields in the region between the black hole and the cosmic horizon. We also demonstrate the existence of at least one type of quantum hair, and of exactly one charged solution for the Abelian Higgs model. Our method of proof can be applied to investigate other types of quantum or topological hair on black holes in the presence of a positive $\Lambda$.