Orbital Signatures of Ultralight Scalars in Binary Black Holes

Abstract

We extend the study of black hole superradiance in binary systems, also known as gravitational atomic physics, to include eccentric and inclined orbits. Such systems exhibit Landau-Zener-like transitions between bound states of the bosonic cloud. We uncover new resonance phenomena, such as early and late resonances, which can grow orbital eccentricity and leave measurable imprints on gravitational-wave signals. To model dynamically formed binaries whose orbital angular momentum is misaligned with the spin of the central black hole, we develop a framework based on Hamiltonian mechanics that couples the full orbital dynamics to the bosonic cloud via multipole interactions. This method resolves limitations of previous balance-law approaches and reveals novel dynamics such as floating on counter-rotating orbits and overlapping resonances. For the first time, we also include non-resonant mixing with states that decay back into the black hole, showing how this alters resonance conditions and suppresses perfect floating, while still leaving significant orbital signatures. For masses of scalar particles from approx. 10^(-13) to 10^(-11) eV, these dynamics leave observable signatures on binary black hole populations, particularly at gravitational wave frequencies accessible to upcoming detectors such as the Laser Interferometer Space Antenna LISA, as well as future mid-band and decihertz detectors.