Can we say it doesn't clump or can we only say it doesn't clump on the galactic scale? Could it clump but then go into it's equivalent of a super nova with very small clumps?
There is a limit to the changes in the momentum of cold dark matter before it produces visible effects in galaxies of different ages. Explosive processes in the dark matter sector must be rare, whatever their mechanism and whatever their daughter products (even if it quickly decays to cold dark matter again, but on a different trajectory).
