Scalar fields of masses between ${10}^{-21}$ and ${10}^{-11}\mathrm{eV}/c^2$ can exhibit enhanced gravitational interactions with black holes and form scalar clouds around them. Such a cloud modifies the dynamics of a coalescing black hole binary, and the resulting gravitational waves may provide a new channel to detect light scalar fields, such as axionlike particles or wavelike dark matter candidates. In this work, we simulate a series of black hole mergers with mass ratios $q=1$ and $q=1/2$, immersed in a scalar field overdensity with masses in the range $M{\mu }_{\mathrm{S}}\in [0,1.0]$. To do so, we implemented a constraint-satisfying initial data solver based on the puncture method, we improved the accuracy of our open-source software canuda to eighth order finite differences, and we reduced the initial orbital eccentricity. We investigate the impact of the scalar mass on the gravitational and scalar radiation. We find that binaries can undergo a delayed or an accelerated merger with respect to vacuum. Our study highlights the challenge and importance of accurately modeling black hole binaries in dark matter environments.

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• Classical black holes
• Dark matter
• Gravitational waves
• Numerical relativity