Parameter space for testable leptogenesis

Extending the Standard Model with right-handed neutrinos provides a minimal explanation for both light neutrino masses (through the type-I seesaw mechanism) and the baryon asymmetry of our universe (through leptogenesis). We map here for the first time the range of heavy neutrino mixing angle consistent with both neutrino masses and leptogenesis in a scenario with 3 generations of right-handed neutrinos with Majorana masses between 50 MeV and 70 TeV. Due to the presence of a third degree of freedom that remains much more feebly coupled to the Standard Model thermal bath, we observe that the parameter space is much larger compared to the minimal scenario with 2 generations. This greatly enhances the testability prospects for low-scale leptogenesis and, in the most optimistic scenario, would allow experimentalists not only to discover right-handed neutrinos but also to perform consistency checks of the model.