Prospects of antideuteron detection from dark matter annihilations or
  decays at AMS-02 and GAPS
  The search for cosmic antideuterons has been proposed as a promising method
to indirectly detect dark matter, due to the very small background flux from
spallations expected at the energies relevant to experiments. The antideuteron
flux from dark matter annihilations or decays is, however, severely constrained
by the non-observation of an excess in the antiproton-to-proton fraction
measured by PAMELA. In this paper we calculate, for representative dark matter
annihilation and decay channels, upper limits on the number of antideuteron
events at AMS-02 and GAPS from requiring that the associated antiproton flux is
in agreement with the PAMELA data. To this end, we first analyze in detail the
formation of antideuterons in the coalescence model using an event-by-event
Monte Carlo simulation and using data from various high energy experiments. We
find that the resulting coalescence momentum shows a dependence on the
underlying process and on the center of mass energy involved. Then, we
calculate, using a diffusion model, the flux of antideuterons at the Earth from
dark matter annihilations or decays. Our results indicate that, despite the
various sources of uncertainty, the observation of an antideuteron flux at
AMS-02 or GAPS from dark matter annihilations or decays will be challenging.
