Implications of triangular features in the Gaia skymap for the Caustic
  Ring Model of the Milky Way halo
  The Gaia map of the Milky Way reveals a pair of triangular features at nearly
symmetric locations on opposite sides of the Galactic Center. In this paper we
explore the implications of these features assuming they are manifestations of
a caustic ring in the dark matter distribution of the Milky Way halo. The
existence of a series of such rings is predicted by the Caustic Ring Model. The
model's phase-space distribution is that acquired by a rethermalizing
Bose-Einstein condensate of axions or axion-like particles. We show that dust
is gravitationally entrained by cold axion flows and propose this as an
explanation for the sharpness of the triangular features. The locations of the
features imply that we on Earth are much closer to the fifth caustic ring than
thought on the basis of pre-Gaia observations. Most likely we are inside its
tricusp cross-section. In that case the dark matter density on Earth is
dominated by four cold flows, termed Big, Little, Up and Down. If we are
outside the tricusp cross-section the dark matter density on Earth is dominated
by two cold flows, Big and Little. We use the triangular features in the Gaia
map, and a matching feature in the IRAS map, to estimate the velocity vectors
and densities of the four locally dominant flows.
