Testing the EoS of dark matter with cosmological observations

TL;DR

This paper uses cosmological observations to constrain the dark matter equation of state parameter w_dm, finding evidence for warm dark matter with w_dm > 0, and also exploring the properties of dark energy.

Contribution

It provides new constraints on w_dm using latest data, indicating warm dark matter and phantom dark energy, expanding understanding of dark matter's properties.

Findings

w_dm is approximately 0.006, indicating warm dark matter

Data favor w_de < -1, suggesting phantom dark energy

Constraints are consistent with previous perturbative analyses

Abstract

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.