  We investigate the production of dark matter with non-standard momentum
distributions arising from the decay of a relativistic massive neutrino into a
lighter fermion and boson H$\rightarrow$F$+$B. We develop the Boltzmann
equations for this process, paying particular attention to spin polarisation
effects. Such decays can, under certain circumstances, lead to a process of
runaway stimulated decays or `neutrino-lasing' resulting, for suitable boson
mass, in the production of mixed-dark-matter. We discuss a number of variations
on the model; we show how the yield of cold particles can be increased by a
simple modification to our original proposal. We discuss the singlet-majoron
model as a possible framework for these decays.
