The Dark Matter at the End of the Galaxy
  Dark matter density profiles based upon Lambda-CDM cosmology motivate an
ansatz velocity distribution function with fewer high velocity particles than
the Maxwell-Boltzmann distribution or proposed variants. The high velocity tail
of the distribution is determined by the outer slope of the dark matter halo,
the large radius behavior of the Galactic dark matter density. N-body
simulations of Galactic halos reproduce the high velocity behavior of this
ansatz. Predictions for direct detection rates are dramatically affected for
models where the threshold scattering velocity is within 30% of the escape
velocity.
