Antimatter in the Universe - constraints from gamma-ray astronomy
Prof. Peter von Ballmoos (CESR, Toulouse)

Antimatter in the Universe can be probed through ordinary matter, with the resulting annihilation gamma-rays providing indirect evidence for its presence. We review the gamma-ray observations that constrain anti- matter - both baryonic and leptonic - in the Universe. Although it is generally accepted that equal amounts of matter and antimatter have been produced in the Big Bang, gamma-rays have so far failed to detect substantial amounts of baryonic antimatter in the Universe. Conversely, positrons are abundantly observed through their annihilation in the central regions of our Galaxy and, while astrophysical sources are plausible, their very origin is still unknown. As both antimatter questions - the source of the Galactic positrons and the baryon asymmetry in the Universe - can be investigated through the low energy gamma-ray channel, the mission concept of a dedicated space telescope is sketched out.