Interacting viscous dark energy in a Bianchi type-Ⅲ universe

We study the evolution of the equation of state of viscous dark energy in the scope of Bianchi type III space-time. We consider a case where the dark energy is minimally coupled to the perfect fluid, as well as in direct interaction with it. The viscosity and the interaction between the two fluids are parameterized by constants 40 and σ, respectively. We have made a detailed investigation of the cosmological implications of this parametrization. To differentiate between different dark energy models, we have performed a geometrical diagnostic by using the statefinder pair {s, r}.

Universe Filled with Generalized Cosmic Chaplygin Gas and Barotropic Fluid

In this paper we have considered a model of the universe filled with Generalized Cosmic Chaplygin Gas and another fluid with barotropic equation of state. We observe its role in accelerating phase of the universe by considering the mixture of these two fluid models valid from the radiation era to for and the radiation era to quintessence model for . The statefinder parameters describe the evolution of the universe in different phases for these two fluid models.

Cosmic acceleration with bulk viscosity in an anisotropic f(R, Lm) background

In this article,we investigate the observed cosmic acceleration in the framework of a cosmological f(R,Lm)model dominated by bulk viscous matter in an anisotropic background.We consider the locally rotationally symmetric Bianchi type I metric and derive the Friedmann equations that drive the gravitational interactions in f((R,Lm)gravity.Further,we assume the functional form f(R,Lm)=R/2+Lαm,where a is a free model parameter,and then find the exact solutions of field equations corresponding to our viscous matter dominated model.We incorporate the updated H(z)data and the Pantheon data to acquire the best-fit values of parameters of our model by utilizing theχ2 minimization technique along with the Markov Chain Monte Carlo random sampling method.Further,we present the behavior of physical parameters that describe the Universe’s evolution phase,such as density,effective pressure and EoS parameters,skewness parameter,and the statefinder diagnostic parameters.We find that the energy density indicates expected positive behavior,whereas the negative behavior of bulk viscous pressure contributes to the Universe’s expansion.The effective EoS parameter favors the accelerating phase of the Universe’s expansion.Moreover,the skewness parameter shows the anisotropic nature of spacetime during the entire evolution phase of the Universe.Finally,from the statefinder diagnostic test,we found that our cosmological f(R,Lm)model lies in the quintessence region,and it behaves like a de-Sitter universe in the far future.We analyze different energy conditions in order to test the consistency of the obtained solution.We find that all energy conditions except strong energy condition(SEC)show positive behavior,while the violation of SEC favors the recently observed acceleration with the transition from decelerated to an accelerated epoch of the Universe’s expansion in the recent past.

A Pressure Parametric Dark Energy Model

In this paper, we propose a new pressure parametric model of the total cosmos energy components in a spatially flat Friedmann-Robertson-Walker(FRW) universe and then reconstruct the model into quintessence and phantom scenarios, respectively. By constraining with the datasets of the type Ia supernova(SNe Ia), the baryon acoustic oscillation(BAO) and the observational Hubble parameter data(OHD), we find that ?_(m0)=0.270_(-0.034)^(+0.039) at the 1σ level and our universe slightly biases towards quintessence behavior. Then we use two diagnostics including Om(a) diagnostic and statefinder to discriminate our model from the cosmology constant cold dark matter(ΛCDM)model. From Om(a) diagnostic, we find that our model has a relatively large deviation from the ΛCDM model at high redshifts and gradually approaches the ΛCDM model at low redshifts and in the future evolution, but they can be easily differentiated from each other at the 1σ level all along. By the statefinder, we find that both of quintessence case and phantom case can be well distinguished from the ΛCDM model and will gradually deviate from each other. Finally,we discuss the fate of universe evolution(named the rip analysis) for the phantom case of our model and find that the universe will run into a little rip stage.

Tsallis agegraphic dark energy model with the sign-changeable interaction

In this paper,we study the evolution of a spatially flat universe composed of Tsallis agegraphic dark energy(TADE)and a pressureless dark matter(DM),by assuming that there is a signchangeable interaction between TADE and DM.The density,deceleration parameter and the equation of state parameters(EoS)show satisfactory behaviors in the model.By analysis we find that the accelerated expansion of the universe can be achieved at the late time if model parametersδ>2 and-2/3<β<0.Also,we investigate the interacting TADE model by means of statefinder diagnostic and w–w’analysis.