Gravitational Signatures of Wave Dark Matter

Abstract

This thesis explores wave dark matter and its intriguing phenomenological implications, namely the presence of wave-like signatures on astrophysical length scales. Specifically, we assume the dark matter is composed of light bosons with masses below 10 eV, allowing, due to the high phase space occupation number, for a classical wave description. We develop a formalism to describe the wave dark matter’s response to gravity, accounting for the statistical properties of the field. Our first subject of investigation is the behavior of the wave dark matter in the Solar system. Here we study the phenomenon of gravitational focusing, where a massive astrophysical object deforms the local distribution of dark matter, leading to a local overdensity. We calculate the response of observationally-motivated dark matter substructures to the Sun’s potential and find unique signatures in the local overdensity and dark matter spectrum that can be relevant for direct detection ex- periments. The second topic of discussion is the behavior of wave dark matter in a small dark matter halo. In particular, we investigate the wave dark matter response to the adiabatic growth of a black hole in the center of the halo. This phenomenon leads to a compression of the surrounding dark matter halo, resulting in a steeper density profile. We find significant wave features in the density profile of the compressed halo’s inner region, where the semiclassical approximation breaks down. As an application, we investigate the gravitational waves produced by the inspiral of a compact solar-mass object with a central intermediate-mass black hole within the compressed wave dark matter halo. Due to the enhanced mass density, the compressed halo exerts dynamical friction on the orbiting object which is stronger than in the uncompressed case, leading to a characteristic dephasing of the gravitational waves. This quantity being sensitive to the underlying dark matter model, we dis- cuss concrete scenarios where the wave dark matter halo can be reconstructed from gravitational wave observations.