Dissipative unified dark fluid model

Abstract

We consider a unified barotropic dark fluid model with dissipation. Our fluid asymptotes between two power laws and so can interpolate between the dust and dark energy (DE) equations-of-state at early and late times. The dissipative part is a bulk viscous part with constant viscosity coefficient. The model is analyzed using the phase-space methodology which helps to understand the dynamical behavior of the model in a robust manner without reference to the system solution. The parameters of the model are constrained through many observational constraints. The model is tested through many physical and observational tests. We first considered the model independent [Formula: see text] test. Results for [Formula: see text] are plotted against the BAO data for this quantity from different authors, which shows that the model is consistent with the data points for the full redshift range. The [Formula: see text] statistics results in the value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. The Hubble parameter equation is solved numerically and results are plotted against the recent set of Hubble data. The [Formula: see text] test with the Hubble data resulted in the [Formula: see text] value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. The distance modulus at different values of redshift is calculated numerically and results are compared to the newest set of SNe Ia data, the Pantheon Sample. We obtained a [Formula: see text] value of [Formula: see text] with a [Formula: see text]-value of [Formula: see text]. These results show that our model is efficiently consistent with observations. The model expectations for the evolution of the universe are also studied by testing the evolution of the deceleration parameter, the density of the universe, and the effective equation-of-state parameter of the model and of its underlying dark energy candidate. The value of the present day viscosity coefficient of the cosmic fluid, [Formula: see text], is estimated. It is found to be [Formula: see text][Formula: see text]Pa[Formula: see text]s. We argue that this model is able to explain the behavior of the universe evolution.