Small-scale structure in vector dark matter
  We investigate the differences in the small-scale structure of vector dark
matter (VDM) and scalar dark matter (SDM) using 3+1 dimensional simulations of
single/multicomponent Schr\"{o}dinger-Poisson system. We find that the amount
of wave interference, core-to-halo mass ratio (and its scatter), spin of the
core, as well as the shape of the central regions of dark matter halos can
distinguish VDM and SDM. Starting with a collection of idealized halos
(self-gravitating solitons) as an initial condition, we show that the system
dynamically evolves to an approximately spherically symmetric configuration
that has a core surrounded by a halo of interference patterns in the mass
density. In the vector case, the central soliton in less dense and has a
smoother transition to an $r^{-3}$ tail compared to the scalar case. As
compared to SDM, wave interference in VDM is $\sim 1/\sqrt{3}$ times smaller,
resulting in fewer low and high density regions, and more diffuse granules in
the halo. The ratio of VDM core mass to the total halo mass is lower than that
in SDM, with a steeper dependence on the total energy of the system and a
slightly larger scatter. Finally, we also initiate a study of the evolution of
intrinsic spin angular momentum in the VDM case. We see a positive correlation
between the total intrinsic spin in the simulation and the spin of the final
central core, with significant scatter. We see large intrinsic spin in the core
being possible even with vanishing amounts total angular momentum in the
initial conditions (at least instantaneously). Our results point towards the
possibility of distinguishing VDM from SDM using astrophysical and terrestrial
observations.
