Ultralight bosons are compelling dark-matter candidates. Both scalar and vector bosons can be produced through black hole superradiance, forming a boson cloud surrounding a rotating black hole. In binary systems, the gravitational perturbation from a companion can trigger various dynamical processes. In this work, we investigate the dynamics of both scalar and vector boson clouds in binary black hole systems. We develop a variational molecular-orbital framework, in which the cloud wave function is expanded using a single bound state of the primary black hole and an extended set of bound states centered on the companion black hole, to study boson-cloud mass transfer in unequal-mass binaries with arbitrary companion-spin orientations. Our results show that mass transfer and subsequent absorption by the companion provide a dominant depletion channel for vector clouds, whereas scalar clouds are primarily depleted by hyperfine mixing into the primary. We identify critical mass ratios below which molecular orbitals fail to form efficiently, and special resonant mass ratios where enhanced binding leads to depletion at larger orbital separations. Furthermore, when the companion’s spin is not aligned with that of the primary, the efficiency of vector cloud depletion is significantly suppressed—a feature absent in the scalar case due to the spherical symmetry of the dominant decaying mode.

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• Classical black holes
• Particle astrophysics
• Particle dark matter