Gravitational Focusing of Wave Dark Matter
  A massive astrophysical object deforms a local distribution of dark matter,
resulting in a local overdensity of dark matter. This phenomenon is often
referred to as gravitational focusing. In the solar system, the gravitational
focusing due to the Sun induces modulations of dark matter signals on
terrestrial experiments. We consider the gravitational focusing of a light
bosonic dark matter with a mass of less than about 10 eV. The wave nature of
such dark matter candidates leads to unique signatures both in the local
overdensity and in the spectrum, both of which can be experimentally relevant.
We provide a formalism that captures both the gravitational focusing and the
stochasticity of wave dark matter, paying particular attention to the
similarity and difference to particle dark matter. Distinctive patterns in the
density contrast and spectrum are observed when the de Broglie wavelength of
dark matter becomes comparable or less than the size of the system and/or when
the velocity dispersion of dark matter is sufficiently small. While
gravitational focusing effects generally remain at a few percent level for a
relaxed halo dark matter component, they could be much larger for dark matter
substructures. With a few well-motivated dark matter substructures, we
investigate how each substructure responds to the gravitational potential of
the Sun. The limit at which wave dark matter behaves similar to particle dark
matter is also discussed.
