Gravitational Wave Resonance in Ultra-Light Dark Matter Halos

Ultra-Light Dark Matter (ULDM) halos constituted by Ultra-Light Axions (ULAs) generate gravitational potentials that oscillate in time. In this paper I show these potentials interact with gravitational waves, resonantly amplifying them. For all ULA masses considered, the resonance in the solar region is currently negligible, while in a denser dark matter environment, which may arise in different scenarios, it might become significant. The frequency of the amplified gravitational wave is equal to the ULA mass in the case of first resonance band, which represents the most efficient scenario.