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The generalized Chaplygin gas, which interpolates between a high densityrelativistic era and a non-relativistic matter phase, is a popular dark energycandidate. We consider a generalization of the Chaplygin gas model, by assumingthe presence of a bulk viscous type dissipative term in the effectivethermodynamic pressure of the gas. The dissipative effects are described byusing the truncated Israel-Stewart model, with the bulk viscosity coefficientand the relaxation time functions of the energy density only. The correspondingcosmological dynamics of the bulk viscous Chaplygin gas dominated universe isconsidered in detail for a flat homogeneous isotropicFriedmann-Robertson-Walker geometry. For different values of the modelparameters we consider the evolution of the cosmological parameters (scalefactor, energy density, Hubble function, deceleration parameter and luminositydistance, respectively), by using both analytical and numerical methods. In thelarge time limit the model describes an accelerating universe, with theeffective negative pressure induced by the Chaplygin gas and the bulk viscouspressure driving the acceleration. The theoretical predictions of theluminosity distance of our model are compared with the observations of the typeIa supernovae. The model fits well the recent supernova data. From the fittingwe determine both the equation of state of the Chaplygin gas, and theparameters characterizing the bulk viscosity. The evolution of the scalar fieldassociated to the viscous Chaplygin fluid is also considered, and thecorresponding potential is obtained. Hence the viscous Chaplygin gas modeloffers an effective dynamical possibility for replacing the cosmologicalconstant, and to explain the recent acceleration of the universe.

Viscous dissipative Chaplygin gas dominated homogenous and isotropic cosmological models