  The lightness of the Standard Model (SM) neutrinos could be understood if
their masses were to be generated by new physics at a high scale, through the
so-called seesaw mechanism involving heavy fermion singlets. If new physics
violates baryon minus lepton number by only a small amount, the heavy fermion
singlets as well as the SM neutrinos split into pairs of quasi-Dirac states. At
the scale of the fermion singlets, this quasi-Diracness allows to enhance CP
violation in their decays and the cosmic matter-antimatter asymmetry can be
successfully generated through resonant leptogenesis. At lower scale, this
quasi-Diracness results in small SM neutrino mass splitting which can be probed
in oscillation experiments. Remarkably, the parameter space for viable
leptogenesis spans over the regime relevant for solar and atmospheric neutrino
oscillations.
