Testing warmness of dark matter

Dark matter (DM) as a pressureless perfect fluid provides a good fit of the standard $\Lambda$CDM model to the astrophysical and cosmological data. In this paper, we investigate two extended properties of DM: a possible time dependence of the equation of state (EoS) of DM via Chevallier-Polarski-Linder parametrization, and the non-null sound speed. We analyze these DM properties using the data from Planck cosmic microwave background (CMB) temperature and polarization anisotropy, the local value of the Hubble constant from the Hubble Space Telescope, and some large scale structure information from the abundance of galaxy clusters, which are in tension with CMB data within the minimal $\Lambda$CDM model. First, we study the minimal $\Lambda$CDM model plus the extended properties of DM, and find more stronger (more closer to the null value) constraint on the EoS of DM, and a weaker constraint on the sound speed, when compared to the recent results in the literature. As a second model, we extend the first case to include also neutrinos properties, and find that this case yields weaker constraints on both the extended properties of DM, in comparison with the results in the literature. Further, we notice that inclusion of neutrinos does not affect extended parameters of DM significantly. Also, we estimate the warmness of DM particles as well as its mass scale, and find a lower bound: $\sim$ 500 eV - 600 eV from our analyzes. Lastly, in all the analyzes carried out here, the EoS and sound speed of the DM are non-null at 68\% CL, but no significant evidence can be stated beyond the standard case, and we conclude that the present observational data favor DM as a pressureless fluid.