Neutrino Masses and Leptogenesis from Extra Fermions

The observable nonzero neutrino masses and baryon asymmetry of the Universe cannot be explained within the minimal Standard Model of particle physics and cosmology. However many Standard Model extensions generate both the baryon asymmetry through Leptogenesis (LG) and the neutrino masses . The model independent upper bound on the CP asymmetry relevant for LG with hierarchical heavy neutrinos is called Davidson-Ibarra bound. I will revise it and show that in the case of one massless neutrino this bound essentially depends on the type of the light neutrino mass hierarchy. I will give the classification of LG scenarios according to the new fermion mass spectra, and discuss resonant scenarios, which help to avoid the problem of too high reheating temperature in the early Universe. In particular, I will introduce freed LG, which violates Davidson-Ibarra bound in a special class of models.