Cold dark matter plus not-so-clumpy dark relics
  Various particle physics models suggest that, besides the (nearly) cold dark
matter that accounts for current observations, additional but sub-dominant dark
relics might exist. These could be warm, hot, or even contribute as dark
radiation. We present here a comprehensive study of two-component dark matter
scenarios, where the first component is assumed to be cold, and the second is a
non-cold thermal relic. Considering the cases where the non-cold dark matter
species could be either a fermion or a boson, we derive consistent upper limits
on the non-cold dark relic energy density for a very large range of velocity
dispersions, covering the entire range from dark radiation to cold dark matter.
To this end, we employ the latest Planck Cosmic Microwave Background data, the
recent BOSS DR11 and other Baryon Acoustic Oscillation measurements, and also
constraints on the number of Milky Way satellites, the latter of which provides
a measure of the suppression of the matter power spectrum at the smallest
scales due to the free-streaming of the non-cold dark matter component. We
present the results on the fraction $f_{\rm ncdm}$ of non-cold dark matter with
respect to the total dark matter for different ranges of the non-cold dark
matter masses. We find that the 2$\sigma$ limits for non-cold dark matter
particles with masses in the range 1--10 keV are $f_{\rm ncdm}\leq0.29$ (0.23)
for fermions (bosons), and for masses in the 10--100 keV range they are $f_{\rm
ncdm}\leq0.43$ (0.45), respectively.
