Testing the EoS of dark matter with cosmological observations
  We explore the cosmological constraints on the parameter w_dm of the dark
matter barotropic equation of state (EoS) to investigate the "warmness" of the
dark matter fluid. The model is composed by the dark matter and dark energy
fluids in addition to the radiation and baryon components. We constrain the
values of w_dm using the latest cosmological observations that measure the
expansion history of the Universe. When w_dm is estimated together with the
parameter w_de of the barotropic EoS of dark energy we found that the
cosmological data favor a value of w_dm = 0.006 +- 0.001, suggesting a -warm-
dark matter, and w_de= -1.11 +- 0.03$ that corresponds to a phantom dark
energy, instead of favoring a cold dark matter and a cosmological constant
(w_dm = 0, w_de = -1). When w_dm is estimated alone but assuming w_de = -1,
-1.1, -0.9, we found w_dm = 0.009 +- 0.002, 0.006 +- 0.002, 0.012 +- 0.002
respectively, where the errors are at 3 sigma (99.73%), i.e., w_dm > 0 with at
least 99.73% of confidence level. When (w_dm, \Omega_dm0) are constrained
together, the best fit to data corresponds to (w_dm=0.005 +- 0.001, \Omega_dm0
= 0.223 +- 0.008) and with the assumption of w_de = -1.1 instead of a
cosmological constant (i.e., w_de = -1). With these results we found evidence
of w_dm > 0 suggesting a -warm- dark matter, independent of the assumed value
for w_{\rm de}, but where values w_de < -1 are preferred by the observations
instead of the cosmological constant. These constraints on w_dm are consistent
with perturbative analyses done in previous works.
