Equation of state of dark matter after Planck data

Abstract

In this paper, we loosen the zero equation of state of dark matter to a constant w_dm. By using the currently available cosmic observations, which include the type-Ia supernovae, the baryon acoustic oscillation, the WiggleZ measurements of matter power spectrum, and the cosmic microwave background radiation from the firs release of Planck data through the Markov chain Monte Carlo method, we found the equation of state of dark matter in 3σ regions: w_dm=0.000707_{-0.000747-0.00149-0.00196}^{+0.000746+0.00146+0.00193}. The difference between the minimum of χ² between the ΛCDM and ΛwDM models is Δχ_min⁡²=0.446 for one extra model parameter w_dm. Although the currently available cosmic observations favor the ΛwDM mildly, no significant deviation from the ΛCDM model is found in 1σ regions.