Speaker
Description
In general relativity, an apparent horizon is commonly used as a quasi-local boundary around a black hole region instead of the event horizon, which is a teleological surface. Apparent horizons have many useful applications in numerical relativity, however, they can be difficult to determine and are foliation dependent, i.e., observer dependent. Recently it has been proven that stationary black holes and dynamical black holes admitting isolated horizons can be determined using the zero-set of a collection of curvature invariants which defines the so-called geometric horizon of these black hole solutions. Motivated by this fact, a set of conjectures have been introduced which propose that a geometric horizon exist in every dynamical black hole spacetime and act as an invariant boundary around the black hole.
While the geometric horizon conjectures have now been verified for other dynamical black hole solutions, there are still ambiguities with the definition of a geometric horizon. To illustrate this problem, I will discuss a spherically symmetric line element which admits either a dynamical black hole geometry or a dynamical wormhole geometry and show that in both cases the apparent horizon and the wormhole throat is partially characterized by a single curvature invariant. In order to distinguish the wormholes from the black holes further conditions must be appended to the original definition. I will show what conditions are needed and discuss how these conditions might be extended beyond spherical symmetry.
