  Energetic antiprotons in cosmic rays can serve as an important indirect
signature of dark matter. Conventionally, the antiproton flux from dark matter
decays or annihilations is calculated by solving the transport equation with a
space-independent diffusion coefficient within the diffusion zone of the
galaxy, and assuming free propagation outside this zone. Antiproton sources
outside of the diffusion zone are ignored. In reality, it is far more likely
that the diffusion coefficient increases smoothly with distance from the disk,
and the outlying part of the dark matter halo ignored in the conventional
approach can be significant, containing as much as 90% of the galactic dark
matter by mass in some models. We extend the conventional approach to address
these issues. We obtain analytic approximations and numerical solutions for
antiproton flux assuming that the diffusion coefficient increases exponentially
with the distance from the disk, and including contributions from dark matter
annihilations/decays in essentially the full dark matter halo. We find that the
antiproton flux predicted in this model deviates from the conventional
calculation for the same dark matter parameters by up to about 25%.

High Energy Astrophysical Phenomena;High Energy Physics - Phenomenology