Constraints on a decomposed dark fluid with constant adiabatic sound speed by jointing the geometry test and growth rate after Planck data

Abstract

In this paper, a unified dark fluid with constant adiabatic sound speed is decomposed into cold dark matter interacting with vacuum energy. Based on a Markov-chain Monte Carlo method, we constrain this model by jointing the geometry and dynamical measurement. The geometry test includes cosmic microwave background radiation from Planck, baryon acoustic oscillation, and type-Ia supernovae; the dynamic measurement is fσ₈(z) data points, which is obtained from the growth rate via redshift space distortion, and σ₈(z) is the root-mean-square amplitude of the density contrast δ at the comoving 8h-¹ Mpc scale. The jointed constraint shows that α =0.000662-0.000662+0.000173 and α₈=0.824-0.0166+0.0128. The CMB and matter power spectra are both similar for the case of α =mean value and that of α=0. However, the evolutionary curves of fσ₈(z) are different. This means that, to some extent, the data points of the growth rate could break the degeneracy of the dark energy models.