Plasma-photon interaction in curved spacetime I: formalism and quasibound states around nonspinning black holes

Understand

We investigate the linear dynamics of an electromagnetic field propagating in curved spacetime in the presence of plasma.

• The dynamical equations are generically more involved and richer than the effective Proca equation adopted as a model in previous work.
• We discuss the general equations and focus on the case of a cold plasma in the background of a spherically-symmetric black hole, showing that the system admits plasma-driven, quasibound electromagnetic states that are prone to become superradiantly unstable when the black hole rotates.
• The quasibound states are different from those of the Proca equation and have some similarities with the case of a massive scalar field, suggesting that the linear instability can be strongly suppressed compared to previous estimates.