High-frequency gravitational wave transients from superradiance

TL;DR

This paper models gravitational waves from ultralight boson clouds around black holes, analyzing signals from isolated and binary systems, and discusses their detectability with future high-frequency gravitational-wave detectors.

Contribution

It provides a unified analytic framework for gravitational-wave emission from gravitational atoms, including binary effects, and assesses their detectability.

Findings

Binary-driven transitions produce transient signals with durations compatible with detectors.

Characteristic strain of signals is below current detector sensitivity at plausible distances.

Detectability requires significant improvements in sensitivity, bandwidth, and response of gravitational-wave detectors.

Abstract

Ultralight bosons can form macroscopic gravitational-atom clouds around rotating black holes via superradiance, sourcing quasi-monochromatic gravitational waves through level transitions and annihilation. Primordial black holes provide a natural setting for such systems in a frequency range relevant for resonant-cavity experiments. We present a unified treatment of gravitational-wave emission from both isolated and binary-perturbed gravitational atoms in this regime. For isolated systems, we derive analytic expressions for the time- and frequency-domain strain from transition and annihilation channels, emphasizing their narrow-band structure. For binaries, we model resonantly driven level transitions using the Landau--Zener formalism and compute the resulting transient signals. We find that, while binary-driven transitions generically yield signals with durations compatible with detector response times, their characteristic strain lies well below the sensitivity of current experiments at astrophysically plausible distances, and event rates further suppress detectability by requiring sources at unrealistically small separations. We quantify the improvements in sensitivity, bandwidth, and response needed to render these signals observable, and identify gravitational-atom systems around primordial black holes as a theoretically well-motivated target for future high-frequency gravitational-wave searches.