New asymptotically flat Einstein--Maxwell instantons

We disprove the Euclidean Einstein–Maxwell Black Hole Uniqueness Conjecture, and thus demonstrate that the semi-classical properties of coupled gravitational and electromagnetic fields are more subtle than expected from Lorentzian general relativity, where the Kerr—Newman family of metrics yields the most general stationary and asymptotically flat black holes with a single event horizon. This is achieved by an explicit construction of a new three–parameter family of asymptotically flat Einstein–Maxwell instantons. These solutions are toric, regular, and free of conical and orbifold singularities on the manifold M = CP2 1. In the case of vanishing charge, these instantons reduce to the Chen–Teo Ricci flat instantons.