  Properties of neutrinos, the lightest of all elementary particles, may be the
origin of the entire matter-antimatter asymmetry of the universe. This requires
that neutrinos are Majorana particles, which are equal to their antiparticles,
and that their masses are sufficiently small. Leptogenesis, the theory
explaining the cosmic matter-antimatter asymmetry, predicts that all neutrino
masses are smaller than 0.2 eV, which will be tested by forthcoming laboratory
experiments and by cosmology.
