Viscous generalized Chaplygin gas as a unified dark fluid

Abstract

In this paper, we revisit viscous generalized Chaplygin gas (VGCG) as a unified dark fluid, which modifies the pressure only by redefining the effective pressure peff, according to \(p_{\mathrm{eff}}=p-\sqrt{3}\zeta_{0}\rho\), where ζ0 is the newly added model parameter which characterizes the viscous property and can be determined by the cosmic observations. By using the currently available cosmic observational data from WMAP, BAO, and SN Ia, the model parameter space is obtained via a Markov Chain Monte Carlo method: \(\zeta_{0}=0.000708_{- 0.00155- 0.00311- 0.00503}^{+ 0.00151+ 0.00275+ 0.00425}\) in 1, 2, 3σ regions. The results show that the viscous effect is very small due the value ζ0≈0 and the VGCG model can match observational data points as well as ΛCDM model.