Cosmic-ray anti-helium nuclei or the quest for antimatter in the Universe
Laboratoire d'Annecy-le-Vieux de Physique Théorique LAPTh
AMS-02 might have discovered in its data a few anti-helium events. To illustrate how problematic these would be, should they be confirmed, we have updated the calculation of the anti-helium cosmic ray fluxes at the Earth from secondary origin. We show that spallation from primary hydrogen and helium nuclei onto the interstellar medium yields an anti-He-3 flux typically one to two orders of magnitude below the sensitivity of AMS-02 after 5 years, and an anti-He-4 flux roughly 5 orders of magnitude below AMS sensitivity. I will present how these secondary anti-helium fluxes have been derived and also comment upon the difficulties of the annihilating dark matter explanation. Then, playing the devil’s advocate, I will contemplate the possibility of anti-matter domains in our Galaxy and discuss the constraints set on them by gamma-ray observations. From a theoretical perspective, the presence of anti-matter in the early Universe also raises insuperable problems. I will conclude by a recap of the standard lore.