Lunch talk on Apr. 24, 2025

“Superradiant Growth Anomaly” in Vectorial Bosonic Condensates Around Kerr Black Holes with Near-Horizon Reflections

Speaker: Guirong Liang (China University of Mining and Technology)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Thursday, Apr. 24, 2025

Abstract: 

Ultralight bosons would form evolving condensates around a rotating black hole (BH) due to superradiant instability, however distinguishing features show up in bounded bosonic fields with non-zero spin: The dominant growing mode with vanishing orbital angular momentum makes the cloud configuration much closer to the BH, hence more sensitive to near-horizon geometry. We study the effect of near-horizon reflection on the evolution of the vectorial bounded system, and report the “superradiant growth anomaly” phenomenon discovered in our recent work: In high-spin BH cases, the superadiance rate is, unexpectedly, temporarily increased by the reflection parameter, and this would leave imprint on the gravitational waveform. We propose mathematical, geometrical, and physical descriptions of this anomaly, with the last one demonstrating the anomaly condition is that information carried away by unit particle superradiated exceeds a certain value determined by the horizon-reflection, and this may provide clues for the BH information evolution. We further constructed three featured quantities to illustrate this anomaly, which are related to the corresponding gravitational wave strain difference. Finally, we will discuss an application of this anomaly: In joint with a specific continuous reflection spectrum, the anomaly makes its “non-monotony” to guide the “medium value selection” of the boson mass, which provides a new perspective to infer BH horizon properties and identify dark matter candidates from gravitational wave signals.

Report PPT:  SWIFAR_Guirong Liang.pdf