Abstract
The superradiant instability of black hole space-times has been used to place limits on ultra-light bosonic particles. We show that these limits are model dependent. While the initial growth of the mode is gravitational and thus model independent, the ability to place a limit on new particles requires the mode to grow unhindered to a large number density. Non-linear interactions between the particle and other light degrees of freedom that are mediated through higher dimension operators can damp this growth, eliminating the limit. However, these non-linearities may also destroy a cosmic abundance of these light particles, an attractive avenue for their discovery in several experiments. We study the specific example of the QCD axion and show that it is easy to construct models where these non-linearities eliminate limits from superradiance while preserving their cosmic abundance.
Highlights
Ultra-light bosonic particles such as axions, axion-like particles, relaxions and hidden photons have attracted significant attention
We have shown that superradiance limits on light particles from measurements of black hole spins are model dependent
While the initial growth of the superradiant modes is due to gravity, the bound requires a large number density of the new particle around the black hole
Summary
Ultra-light bosonic particles such as axions, axion-like particles, relaxions and hidden photons have attracted significant attention. We point out that if the QCD axion has an additional technically natural axion-like interaction with a dark sector that consists of a light (massless) dark photon and a fermion, these additional interactions can completely eliminate superradiance limits on the axion from rotating black holes, while preserving its cosmic abundance. The fermions in the dark sector are assumed to have a cosmic abundance; this abundance yields a plasma mass for the hidden photon in the early Universe, preventing these nonlinearities from affecting the evolution of the dark matter axion. This does not happen around black holes today since these fermions do not have a significant number density around them.. We take fγ0 ≈ 1011 GeV, with q and mψ in the range shown in
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
