Testing the low scale seesaw and leptogenesis
  Heavy neutrinos with masses below the electroweak scale can simultaneously
generate the light neutrino masses via the seesaw mechanism and the baryon
asymmetry of the universe via leptogenesis. The requirement to explain these
phenomena imposes constraints on the mass spectrum of the heavy neutrinos,
their flavour mixing pattern and their $CP$ properties. We first combine bounds
from different experiments in the past to map the viable parameter regions in
which the minimal low scale seesaw model can explain the observed neutrino
oscillations, while being consistent with the negative results of past searches
for physics beyond the Standard Model. We then study which additional
predictions for the properties of the heavy neutrinos can be made based on the
requirement to explain the observed baryon asymmetry of the universe. Finally,
we comment on the perspectives to find traces of heavy neutrinos in future
experimental searches at the LHC, NA62, BELLE II, T2K, SHiP or a future high
energy collider, such as ILC, CEPC or FCC-ee. If any heavy neutral leptons are
discovered in the future, our results can be used to assess whether these
particles are indeed the common origin of the light neutrino masses and the
baryon asymmetry of the universe. If the magnitude of their couplings to all
Standard Model flavours can be measured individually, and if the Dirac phase in
the lepton mixing matrix is determined in neutrino oscillation experiments,
then all model parameters can in principle be determined from this data. This
makes the low scale seesaw a fully testable model of neutrino masses and
baryogenesis.
