Black hole spin constraints on the mass spectrum and number of axionlike fields

Astrophysical observations of spinning black holes, which span 5M MBH 5×108 M, can be used to exclude the existence of certain massive bosons via the superradiance phenomenon. In this work, we explore for the first time how these measurements can be used to constrain properties of statistical distributions for the masses of multiple bosonic fields. Quite generally, our methodology excludes Nax30 scalar fields with a range of mass distribution widths and central values spanning many orders of magnitude. We demonstrate this for the specific example of axions in string theory and M-theory, where the mass distributions in certain cases take universal forms. We place upper bounds on Nax for certain scenarios of interest realized approximately as mass distributions in M-theory, including the QCD axion, grand unified theories, and fuzzy dark matter.