  Antideuteron and antihelium nuclei have been proposed as a detection channel
for dark matter annihilations and decays in the Milky Way, due to the low
astrophysical background expected. To estimate both the signal for various dark
matter models and the astrophysical background, one employs usually the
coalescence model in a Monte Carlo framework. This allows one to treat the
production of antinuclei on an event-by-event basis, taking thereby into
account momentum correlations between the antinucleons involved in the process.
This approach lacks however an underlying microscopic picture, and the
numerical value of the coalescence parameter obtained from fits to different
reactions varies considerably. Here we propose instead to combine
event-by-event Monte Carlo simulations with a microscopic coalescence picture
based on the Wigner function representations of the produced antinuclei states.
This approach allows us to include in a semi-classical picture both the size of
the formation region, which is process dependent, and momentum correlations.
The model contains a single, universal parameter which is fixed by fitting the
production spectra of antideuterons in proton-proton interactions, measured at
the Large Hadron Collider. Using this value, the model describes well the
production of various antinuclei both in electron-positron annihilation and in
proton-proton collisions.
