Early Universe Hypercharge Breaking and Neutrino Mass Generation.

We show that the conditions allowing for a spontaneous breaking of the U(1)_{Y} hypercharge gauge symmetry of the standard model (SM) in the early Universe are generically present in extensions of the SM addressing the generation of light neutrino masses via radiative contributions. In such scenarios, the breaking of (hyper)charge at high temperatures yields new possibilities for explaining the observed matter-antimatter asymmetry of the Universe. Considering for concreteness the Zee-Babu radiative neutrino mass generation model, we show that a period of hypercharge breaking prior to the electroweak phase transition could allow for successful baryogenesis via a nonconventional leptogenesis mechanism, based on the presence of charge-breaking masses for the SM leptons in the early Universe.