Black hole superradiance to search for new particles

Abstract: Rotational superradiance generates the amplification of incoming waves of sufficiently low frequency when scattered with a rotating absorbing body. This may be used to discover new \emph{bosonic} particles of mass $m_b$ if the rotating body has a sufficiently strong gravitational field, that may confine the massive particle and turn amplification into exponential growth. As a result, the initial seed may be amplified until generating a large cloud around the body, which may have a number of phenomenological consequences. Rotating black holes are perfect candidates to source this effect, not only from their absorbing and gravitational properties (and hence confining mechanism), but also because for black holes of mass $M_{\rm BH}$, rotational superradiance is efficient for $m_b\sim 10^{-10}\left(\frac{M_{\odot}}{M_{\rm BH}}\right)\rm eV$. The wide range of astrophysical black hole masses brings about new opportunities to probe particles of low masses in a large span very hard to detect by any other known method. In this brief contribution I will comment on some of these opportunities.