Neutrino masses from Planck scale lepton number breaking

Adding heavy right-handed neutrinos to the Standard Model particle content is a simple and compelling explanation for the small neutrino masses inferred from oscillation experiments. On the other hand, this framework contains many free parameters and the neutrino masses cannot be predicted. In this talk we construct a simple seesaw framework where the lepton number is broken at the Planck scale, and we argue that under some plausible conditions this framework naturally leads to one active neutrino mass in the ballpark of the experimental values. We also comment on the generation of the mild hierarchy between the solar and atmospheric neutrino mass scales.