Statefinder Parameters for Coupled Quintessence Scenario in a Power Law Case

We investigate a coupled quintessence scenario, which can provide a natural solution to the cosmic coincidence problem. We assume that the mass of dark matter particles depends on a power law function of the scalar field associated to dark energy and meanwhile the scalar field evolves in a power law potential. Since the dynamics of this system is dominated by an attractor solution, the mass of dark matter particles is forced to change with time as to ensure that the ratio between the energy densities of dark matter and dark energy becomes a constant at late times,and one thus solves the cosmic coincidence problem naturally. We then apply a statefinder diagnostic to this coupled quintessence scenario. It is shown that the evolving trajectory of this scenario in the s-r diagram is quite different from those of other dark energy models.

Statefinder Diagnosis for the Extended Holographic Ricci Dark Energy Model without and with Interaction

We apply the statefinder diagnostic to the extended holographic Ricci dark energy (ERDE) model without and with interaction to study their behaviors. We plot the trajectories of various parameters for different cases. It is shown that the non-interacting model does not reach the LCDM point {1, 0 } and the interacting one is favored, because the interaction makes the evolution of the statefinder pair r, s quite different.

An Interacting Two-Fluid Scenario for Quintom Dark Energy

The Quintom dark energy is a proposal that explains the recent observations that mildly favor the equation of state of dark energy ω crossing -1 near the past. The Quintom model is often constructed by two scalar fields, where one is the quintessence feld and another is the phantom field. The cosmological implication of the coupling of the two fields of the dark energy is out of question worth investigating. However, the consideration of the coupling in the field scenario is somewhat complex thus we propose an interacting two-fluid Quintom scenario for simplicity. The interaction between the two components is parametrized by a constant 71 in this scenario. The cosmological implications of this parametrization are investigated in detail in this paper. Also, a diagnostic for this model is performed by using the statefinder pairs {s, r} and {q, r}.

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.

Constraining the lattice fluid dark energy from SNe Ia,BAO and OHD

Sanchez and Lacombe have developed a lattice fluid theory based on a well-defined statistical mechanical model.Taking the lattice fluid as a candidate of dark energy,we investigate the cosmic evolution of this fluid.Using the combined observational data of Type Ia Supernova(SNe Ia) Union2.1,Baryon Acoustic Oscillations(BAO) data from 6dFGS,SDSS and WiggleZ survey,and Observational Hubble Data(OHD),we find the best fit value of the parameters:A = 0.3 ± 0.2(1σ) ± 0.4(2σ) ± 0.8(3σ) and Ω m = 0.31 ± 0.02(1σ) ± 0.05(2σ) ± 0.07(3σ).The cosmological implications of the model are presented.

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.

Effects of Low Anisotropy on Generalized Ghost Dark Energy in Galileon Gravity

The definition of the Galileon gravity form is extended to the Brans-Dicke theory. Given, the framework of the Galileon theory, the generalized ghost dark energy model in an anisotropic universe is investigated. We study the cosmological implications of this model. In particular, we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy in Bianchi type I model. We also probe observational constraints by using the latest observational data on the generalized ghost dark energy models as the unification of dark matter and dark energy. In order to do so, we focus on observational determinations of the Hubble expansion rate(namely, the expansion history) H(z). As a result, we show the influence of the anisotropy(although low) on the evolution of the universe in the statefinder diagrams for Galileon gravity.