Entanglement of all pairs of black hole horizons with a common interior

Determine whether all pairs of black hole horizons that share a common interior in spacetimes with arbitrary asymptotic boundary conditions are entangled.

Background

The authors note that specific processes, such as black hole pair production via gravitational instantons in an electromagnetic field, produce highly entangled extremal Reissner–Nordström black holes. They then raise the broader question of whether this entanglement property extends universally to any pair of horizons that share a common interior, independent of the spacetime’s asymptotics. This motivates their investigation connecting black hole complementarity and traversable wormholes to argue for generic entanglement.