  It has been proposed that in a part of the parameter space of the Standard
Model completed by three generations of keV...GeV right-handed neutrinos,
neutrino masses, dark matter, and baryon asymmetry can be accounted for
simultaneously. Here we numerically solve the evolution equations describing
the cosmology of this scenario in a 1+2 flavour situation at temperatures $T
\le 5$ GeV, taking as initial conditions maximal lepton asymmetries produced
dynamically at higher temperatures, and accounting for late entropy and lepton
asymmetry production as the heavy flavours fall out of equilibrium and decay.
For 7 keV dark matter mass and other parameters tuned favourably, $\sim 10\%$
of the observed abundance can be generated. Possibilities for increasing the
abundance are enumerated.
