Cold and Hot Dark Matter from a Single Nonthermal Relic
  The origin of dark matter in the universe may be scalar particles produced by amplification of quantum fluctuations during a period of dilaton-driven inflation. We show, for the first time, that a single species of particles, depending on its mass and interactions, can be a source of both cold and hot dark matter simultaneously. Detection of such weakly interacting particles with masses below a fraction of an eV presents a new challenge for dark matter searches. 
Ram Brustein, Merav Hadad