Anti-helium from Dark Matter annihilations
  Galactic Dark Matter (DM) annihilations can produce cosmic-ray anti-nuclei
via the nuclear coalescence of the anti-protons and anti-neutrons originated
directly from the annihilation process. Since anti-deuterons have been shown to
offer a distinctive DM signal, with potentially good prospects of detection in
large portions of the DM-particle parameter space, we explore here the
production of heavier anti-nuclei, specifically anti-helium. Even more than for
anti-deuterons, the DM-produced anti-He flux can be mostly prominent over the
astrophysical anti-He background at low kinetic energies, typically below 3-5
GeV/n. However, the larger number of anti-nucleons involved in the formation
process makes the anti-He flux extremely small. We therefore explore, for a few
DM benchmark cases, whether the yield is sufficient to allow for anti-He
detection in current-generation experiments, such as AMS-02. We account for the
uncertainties due to the propagation in the Galaxy and to the uncertain details
of the coalescence process, and we consider the constraints already imposed by
anti-proton searches. We find that only for very optimistic configurations it
might be possible to achieve detection with current generation detectors. We
estimate that, in more realistic configurations, an increase in experimental
sensitivity at low-kinetic energies of about a factor of 500-1000 would allow
to start probing DM through the rare cosmic anti-He production.
