Near-horizon microstructure and superradiant instabilities of black holes

Ultralight bosons, as important candidates of dark matter, can condense around spinning black holes (BHs) to form long-lived ``boson clouds'' due to superradiant instabilities. The boson-BH system can be observed through gravitational wave detection and may become a new window to find traces of ultralight bosons. In this paper, we explore the effects on the superradiant instabilities of BHs from the near-horizon microstructure. By introducing the reflection parameter near a BH horizon, we derive analytical results on the corrections to both energy levels of the bosonic cloud and its characteristic frequencies of superradiant instabilities. Our results imply that the evolution of a boson-BH system and the gravitational waves it emits would be influenced by the near-horizon physics of a BH.