Gravitational atoms in the braneworld scenario
General relativity (GR) may be modified by adding an extra warped noncompact spatial dimension such that it is indistinguishable from GR as far as local tests of gravity are concerned. However, such a modified theory of gravity should have intriguing consequences on various aspects of black holes which can help us probe how the presence of an extra dimension affects gravity in the strong field regime, and help us distinguish it from GR. Therefore, we have studied massive scalar perturbations of four-dimensional rotating black holes in the Randall Sundrum II braneworld scenario. These black holes are endowed with a tidal charge that contains information pertaining to the extra spatial dimension in the braneworld model. Such black hole spacetimes are also noteworthy because they permit the black hole's rotation parameter to exceed unity, a possibility strictly forbidden by the general theory of relativity. Consequently, they offer valuable insights into exploring the repercussions of modifications to Einstein's theory through possible future observations. Our approach involves the numerical solution of the perturbed field equations using the continued fractions method. First we ascertain the quasinormal mode spectra of the rotating braneworld black hole. We then thoroughly investigate the existence of quasibound states and the associated superradiant instability. Such a superradiant cloud of bosons around the black hole are called gravitational atoms and are invaluable observational probes of ultralight bosonic particles predicted in various extensions of the Standard Model of particle physics. In comparison to four-dimensional Kerr black hole, we report distinctive signatures of the tidal charge and the rotation parameter, which manifest as signals of the extra dimension on both the quasinormal mode and the formation of gravitational atoms.