Observational probes of the matter-antimatter asymmetry in the Universe

Le 19 septembre 2025, Luigi Tibaldo, 11h45 à 12h45, Salle Jules Verne, OMP, site Belin

Summary: The fundamental laws of physics known to date suggest that equal amounts of matter and antimatter should have been produced, and annihilated, during the Big Bang. Yet, cosmic-ray measurements and gamma-ray observations show that antimatter is present at most in tiny traces is the Solar System and Milky Way neighbourhood. Furthermore the cosmic gamma-ray and microwave backgrounds and the abundances of light elements from Big-Bang nucleosynthesis testify that a perfect symmetry between matter and antimatter is ruled out at the scale of the entire Universe. In this seminar I will provide a review on the observations that characterise the matter-antimatter asymmetry in the Universe and I will discuss some theories that try to explain it. I will then conclude by presenting some recent observational results that may indicate cracks in the current paradigm that the Universe has been free of antimatter domains since its early phases.