Bayesian statistics and parameter constraints on the generalized Chaplygin gas model using SNe Ia data

摘要

The type Ia supernovae (SNe Ia) observational data axe used to estimate the parameters of a cosmological model with cold dark matter and the generalized Chaplygin gas model (GCGM). The GCGM depends essentially on five parameters: the Hubble constant, the parameter (A) over bar related to the velocity of the sound, the equation of state parameter alpha, the curvature of the Universe and the fraction density of the generalized Chaplygin gas (or the cold dark matter). The parameter a is allowed to take negative values and to be greater than one. The Bayesian parameter estimation yields alpha = -0.86(-0.15)(+6.01), H-0 = 62.0(-1.42)(+1.32) km/Mpc.s, Omega(kappa 0) = -0.74(-1.32)(+1.42), Omega(m0) = 0.00(-0.00)(+0.86), Omega(c0) = 1.39(-1.25)(+1.21), (A) over bar = 1.00(-0.39)(+0.00), t(0) = 15.3(-3.2)(+4.2) and qo = -0.80(-0.62)(+0.86), where t(o) is the age of the Universe and qo is the value of the deceleration parameter today. Our results indicate that a Universe completely dominated by the generalized Chaplygin gas is favored, which reinforces the idea that the this gas may unify the description for dark matter and dark energy, at least as far as the SNe Ia data is concerned. A closed and accelerating Universe is also favored. The traditional Chaplygin gas model (CGM), alpha = 1 is not ruled out, even if it does not give the best-fitting. Particular cases with four or three independent free parameters are also analyzed.