Gravitational waves from binary black holes in a self-interacting scalar dark matter cloud

Abstract: We investigate the imprints of accretion and dynamical friction on the gravitational-wave signals emitted by binary black holes embedded in a scalar dark matter cloud. As a key feature in this work, we focus on scalar fields with a repulsive self-interaction that balances against the self-gravity of the cloud. To a first approximation, the phase of the gravitational-wave signal receives extra correction terms at $-3$PN, $-4$PN and $-5.5$PN orders, relative to the prediction of vacuum general relativity, due to cloud gravity, accretion and dynamical friction. Future observations by LISA and B-DECIGO have the potential to detect these effects for a large range of scalar masses~$m_\mathrm{DM}$ and self-interaction couplings~$\lambda_4$. This would correspond to scenarios with dark matter clouds smaller than $0.1$ pc, which would be difficult to detect by other probes.