  Leptogenesis constitues a very simple scenario to achieve the baryon
asymmetry that we observe today. It requires only the presence of right handed
neutrinos (which arise very naturally in many extensions of the Standard Model)
and depends crucially on the mechanism responsible for their production. In
particular, when their mass exceeds the inflaton mass (10^13 GeV in chaotic
inflation) only non perturbative production can occur. It is shown here that
non perturbative production of fermions in an expanding Universe is a very
efficient mechanism up to masses of order of (10^17 - 10^18) GeV, and that it
can be easily applied to solve the baryon asymmetry problem.
