Unstable marginally outer trapped surfaces in static spherically symmetric spacetimes

Understand

We examine potential deformations of inner black hole and cosmological horizons in Reissner-Nordstr\"om de-Sitter spacetimes.

• While the rigidity of the outer black hole horizon is guaranteed by theorem, that theorem applies to neither the inner black hole nor past cosmological horizon.
• Further for pure deSitter spacetime it is clear that the cosmological horizon can be deformed (by translation).
• For specific parameter choices, it is shown that both inner black hole and cosmological horizons can be infinitesimally deformed.