  The existence of baryon asymmetry and dark matter in the Universe may be
related to CP-violating reactions of three heavy neutral leptons (HNLs) with
masses well below the Fermi scale. The dynamical description of the lepton
asymmetry generation, which is the key ingredient of baryogenesis and of dark
matter production, is quite complicated due to the presence of many different
relaxation time scales and the necessity to include quantum-mechanical coherent
effects in HNL oscillations. We derive kinetic equations accounting for fermion
number violating effects missed so far and identify one of the domains of HNL
masses that can potentially lead to large lepton asymmetry generation boosting
the sterile neutrino dark matter production.
