  Rapidly rotating black holes are known to develop instabilities in the
presence of a sufficiently light boson, a process which becomes efficient when
the boson's Compton wavelength is roughly the size of the black hole. This
phenomenon, known as black hole superradiance, generates an exponentially
growing boson cloud at the expense of the rotational energy of the black hole.
For astrophysical black holes with $M \sim \mathcal{O}(10) \, M_\odot$, the
superradiant condition is achieved for bosons with $m_b \sim
\mathcal{O}(10^{-11} ) \, {\rm eV}$; intriguingly, photons traversing the
intergalactic medium (IGM) acquire an effective mass (due to their interactions
with the ambient plasma) which naturally resides in this range. The
implications of photon superradiance, i.e. the evolution of the superradiant
photon cloud and ambient plasma in the presence of scattering and particle
production processes, have yet to be thoroughly investigated. Here, we
enumerate and discuss a number of different processes capable of quenching the
growth of the photon cloud, including particle interactions with the ambient
electrons and back-reactions on the effective mass (arising e.g. from thermal
effects, pair-production, ionization of of the local background, and
modifications to the dispersion relation from strong electric fields). This
work naturally serves as a guide in understanding how interactions may allow
light exotic bosons to evade superradiant constraints.
