http://arxiv.org/abs/2108.10905
We adopt a standard FRW cosmology with a unified scenario, where the usual dark matter and dark energy sectors are replaced by a single dissipative unified dark fluid (DUDF). The equation of state of such fluid can asymptote between two power laws. As a result, it enables fluid to have a smooth transition from dust at early times to dark energy at late times. The dissipation is represented by a bulk viscosity with a constant coefficient, whereas shear viscosity is excluded due to the isotropy of the universe. We performed a Likelihood analysis using recent observational datasets from BAO, CMB, Cosmic Chronometer measurements, and Type Ia supernovae to put cosmological constraints on the model. We found that the viscosity coefficient is not constrained by the data, whence the analysis is continued with this coefficient fixed.
The model yields a minimum $\chi^2$-value of $1357.91$ compared to $1363.34$ for the $\Lambda$CDM model. Using the Akaike Information Criterion (AIC) we found that our model minimizes the AIC value with a difference of -1.4 compared to the $\Lambda$CDM model, which indicates that DUDF model is viable according to background observations. We studied the evolution of the universe due to DUDF model by studying the evolution of different cosmological parameters like the Hubble parameter, the distance modulus, the deceleration parameter, the effective equation of state parameter, and the density parameter. We show that DUDF model doesn’t deviate from the standard $\Lambda$CDM model at early times, with the ability to play the role of the cosmological constant by accelerating the universe in the late times.
E. Elkhateeb and M. Hashim
Thu, 26 Aug 21
17/52
Comments: 20 page, 12 figures
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