Black Holes as laboratories for fundamental physics: Superradiant instabilities

ABSTRACT: It is well known that spinning black holes (BHs) are unstable under ultralight massive bosonic perturbations. Due to this so-called superradiant instability, a macroscopic bosonic condensate can form around the BH, leading to striking observable signatures, such as the emission of detectable gravitational waves from the condensate itself.

Hence, this phenomenon represents a powerful tool to probe ultralight fields beyond the Standard Model, such as axions or dark photons. Until recently, studies of the instability assumed the superradiant field to be free from interactions, aside from a minimal coupling to gravity. However, as number densities can reach extreme values in the process, the effect of interactions can be crucial, even for very feebly interacting fields.

In particular, interactions with the ambient plasma environment (namely an accretion disk or interstellar plasma) or couplings to other Standard Model fields can dramatically change the evolution of these systems. In this talk, I will describe the role of interactions and environmental effects in different superradiant systems, showing their impact in the evolution of the instabilities.