The Hartle–Hawking–Israel state on spacetimes with stationary bifurcate Killing horizons
Abstract
We consider a free massive quantized Klein–Gordon field in a spacetime (M,g) containing a stationary bifurcate Killing horizon, i.e. a bifurcate Killing horizon whose Killing vector field is globally time-like in the right wedge ℳ+ associated to the horizon.
We prove the existence of the Hartle–Hawking–Israel (HHI) vacuum state, which is a pure state on the whole spacetime whose restriction to ℳ+ is a thermal state ωTH for the time-like Killing field at Hawking temperature TH=κ(2π)−1, where κ is the surface gravity of the horizon.
We show that the HHI state is a Hadamard state and is the unique Hadamard state which is equal to the double T−1H-KMS state in the double wedge ℳ−∪ℳ+. We construct the HHI state by Wick rotation in Killing time coordinates, using the notion of the Calderón projector for elliptic boundary value problems.