Antimatter cosmic rays

The dark matter puzzle is still one of the unsolved mysteries of astronomy. Most of the matter in the universe is not visible and its nature remains unresolved. A fraction of it could be made of massive and weakly interacting particles. The favoured candidate is the lightest species of a new realm of particles predicted by the theory of supersymmetry. The latter is actively tested at accelerators. Another main question in cosmology is the existence of a possible asymmetry between matter and antimatter. The current wisdom is that we live in a matter dominated universe and that antimatter islands seem to be excluded. The observation of antiprotons and, more generally, of antinuclei in the cosmic radiation provides a unique tool to address all these issues. Antiprotons are produced naturally by the spallation of cosmic-ray protons with the interstellar gas. A low-energy component would nevertheless provide some evidence for new physics such as the existence of supersymmetric dark matter. A few antideuterons should be collected by the next generation of cosmic-ray detectors whereas the discovery of a single antihelium would be a smoking gun for the existence of antimatter domains. (C) 1999 Elsevier Science B.V. All rights reserved.