Extended Analysis on New Generalized Chaplygin Gas

We extend the study of the new generalized Chaplygin gas （NGCG） based on [J. Cosmol. Astropart. Phys. 0601 （2006） 003]. Specifically, we not only discuss the change rates of the energy densities and the energy transfer of this model, but also perform the Om diagnostic to differentiate the ACDM model from the NGCG and the GCG models. Furthermore, in order to consider the influence of dark energy on structure formation, we also present the evolution of the growth index in this scenario with interaction.     

A Single Model of Interacting Dark Energy: Generalized Phantom Energy or Generalized Chaplygin Gas

I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas, while phantom energy is ruled out as a dark energy candidate.     

Interacting Entropy-Corrected Holographic Chaplygin Gas Model

Holographic dark energy (HDE), presents a dynamical view of dark energy which is consistent with the observational data and has a solid theoretical background. Its definition follows from the entropy-area relation S(A), where S and A are entropy and area respectively. In the framework of loop quantum gravity, a modified definition of HDE called “entropy-corrected holographic dark energy” (ECHDE) has been proposed recently to explain dark energy with the help of quantum corrections to the entropy-area relation. Using this new definition, we establish a correspondence between modified variable Chaplygin gas, new modified Chaplygin gas and the viscous generalized Chaplygin gas with the entropy corrected holographic dark energy and reconstruct the corresponding scalar potentials which describe the dynamics of the scalar field.     

Interacting Generalized Cosmic Chaplygin Gas in Loop Quantum Cosmology: A Singularity Free Universe

In this work we investigate the background dynamics when dark energy is coupled to dark matter with a suitable interaction in the universe described by Loop quantum cosmology. Dark energy in the form of Generalized Cosmic Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is taken into account in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence problem is taken. The statefinder parameters are also calculated to classify the dark energy model. Graphs and phase diagrams are drawn to study the variations of these parameters. It is seen that the background dynamics of Generalized Cosmic Chaplygin gas is completely consistent with the notion of an accelerated expansion in the late universe. From the graphs, generalized cosmic Chaplygin gas is identified as a dark fluid with a lesser negative pressure compared to Modified Chaplygin gas, thus supporting a ‘No Big Rip’ cosmology. It has also been shown that in this model the universe follows the power law form of expansion around the critical point, which is consistent with the known results. Future singularities that may be formed in this model as an ultimate fate of the universe has been studied in detail. It was found that the model is completely free from any types of future singularities.     

Evolution of Variable Generalized Chaplygin Gas

We consider the variable Generalized Chaplygin gas （VGCG） proposal for unification of dark matter and dark energy with p = pdc and ρ= pdm ＋ ρdc. The equation of state of the VGCG is given by p = -A0a^-n/ρ^α, where a is the scale factor. Some cosmological quantities such as the fractional contributions of different components of the universe Ωi （i respectively denotes baryons, dark matter and dark energy） to the critical density, the deceleration parameter q are all obtained. The transition from deceleration to acceleration is described in this model. In addition, we find the behaviour of variable Generalized Chaplgin gas is similar to dust-like matter at early times and will be quiessence or phantom at late stage.     

Thermodynamics of Chaplygin Gas Interacting with Cold Dark Matter

The main goal of the present work is to investigate the validity of the second law of gravitational thermodynamics in an expanding Gödel-type universe filled with generalized Chaplygin gas interacting with cold dark matter. By assuming the Universe as a thermodynamical system bounded by the apparent horizon, and calculating separately the entropy variation for generalized Chaplygin gas, cold dark matter and for the horizon itself, we obtained an expression for the time derivative of the total entropy. We conclude that the 2nd law of gravitational thermodynamics is conditionally valid in the cosmological scenario where the generalized Chaplygin gas interacts with cold dark matter.     

Viscous Generalized Chaplygin Gas in Non-flat Universe

In this paper we study viscous generalized Chaplygin gas and obtain modified Friedmann equations due to viscosity. In the case of non-flat universe we calculate time-dependent energy density of generalized Chaplygin gas. By using stability condition and speed of sound we find critical value of viscosity coefficient where speed of sound is finite.     

Anisotropic Inflationary Scenario Via Generalized Chaplygin Gas Model

We investigate generalized chaplygin gas for warm inflationary scenario in the context of locally rotationally symmetric Bianchi type I universe model.We assume two different cases of dissipative coefficient,i.e.,constant as well as function of scalar field.We construct dynamical equations as well as a relationship between scalar and radiation energy densities under slow-roll approximation.We also derive slow-roll parameters,scalar and tensor power spectra,scalar spectral index,tensor to scalar ratio for analyzing inflationary background during high dissipative regime.We also use the WMAP7 data for the discussion of our parameters.     

Generalized Chaplygin Gas Model as a New Agegraphic Dark Energy in Non-flat Universe

In this paper we consider a correspondence between the new agegraphic dark energy density and generalized Chaplygin gas energy density in non-flat FRW universe. Then we reconstruct the potential and the dynamics of the scalar field which describe the generalized Chaplygin cosmology.     

Evolution of Holographic Dark Energy in Interacting Modified Chaplygin Gas Model

We investigate the modified Chaplygin gas （MCG） with interaction between holographic dark energy proposed by Li and dark matter. In this model, evolution of the universe is described in detail, which is from deceleration to acceleration. Specifically, the evolutions of related cosmological quantities such as density parameter, the equation of state of holographic dark energy, deceleration parameter and transition redshift are discussed. Moreover, we also give their present values which are consistent with the lately observations. Furthermore, the results given by us show such a model can accommodate a transition of the dark energy from a normal state wx 〉 -1 to ωx 〈 -1 phantom regimes.     

Interacting Viscous Modified Chaplygin Gas Cosmology in Presence of Cosmological Constant

Here, we consider interacting viscous modified Chaplygin gas in presence of cosmological constant. We assumed bulk viscosity as a function of density. We consider interaction between modified Chaplygin gas and baryonic matter. Then, the effects of viscosities on the cosmological parameters such as energy, density, Hubble expansion parameter, scale factor and deceleration parameter investigated. This model may be considered as a toy model of our universe.     

Interacting Modified Cosmic Chaplygin Gas with Variable Cosmological Constant and Viscosity

In this paper we study interaction between modified cosmic Chaplygin gas and pressureless matter in presence of both bulk and shear viscosities as a model of our Universe. Also we consider variable cosmological constant and investigate some cosmological parameters such as sound speed and time-dependent density. We investigate stability of model by using first order linear perturbation.     

Generalized Chaplygin Gas Dominated Anisotropic Bianchi Type-I Cosmological Models

We present Bianchi type-I cosmological models in the presence of generalized Chaplygin gas and perfect fluid for early and late time epochs. Exact solutions of Einstein’s field equations for this model are obtained. The general solutions of gravitational field equations are expressed in an exact parametric form, with average scale factor as parameter. In the limiting cases of small and large values of the average scale factor, the solutions of the field equations are expressed in exact analytic forms. Moreover, this model predicts that the expansion of Universe is accelerating for the late times. The physical and geometrical properties of the corresponding cosmological models are discussed.     

Effect of Varying Bulk Viscosity on Generalized Chaplygin Gas

In this paper, viscous generalized Chaplygin gas as a model of dark energy considered. We assume non-constant bulk viscous coefficient and study dark energy density. We consider several cases of density-dependent viscosities. We find that, in the special case, the viscous generalized Chaplygin gas is corresponding to modified Chaplygin gas.     

Letter: Gravitational Waves in the Generalized Chaplygin Gas Model

The consequences of taking the generalized Chaplygin gas as the dark energy constituent of the Universe on the gravitational waves are studied and the spectrum obtained from this model, for the flat case, is analyzed. Besides its importance for the study of the primordial Universe, the gravitational waves represent an additional perspective (besides the CMB temperature and polarization anisotropies) to evaluate the consistence of the different dark energy models and establish better constraints to their parameters. The analysis presented here takes this fact into consideration to open one more perspective of verification of the generalized Chaplygin gas model applicability. Nine particular cases are compared: one where no dark energy is present; two that simulate the -CDM model; two where the gas acts like the traditional Chaplygin gas; and four where the dark energy is the generalized Chaplygin gas. The different spectra permit to distinguish the -CDM and the Chaplygin gas scenarios.     

Viscous Varying Generalized Chaplygin Gas with Cosmological Constant and Space Curvature

In this paper we study varying generalized Chaplygin gas which has viscosity in presence of cosmological constant and space curvature. By using well-known forms of scale factor in non-linear differential equation we obtain behavior of dark energy density numerically. We use observational data to fix solution and discuss about stability of our system.     

Statefinder Diagnostic for Variable Generalized Chaplygin Gas with the Sign-Changeable Interaction

In this paper, we apply the statefinder diagnostic to variable generalized Chaplygin gas (VGCG) with the sign-changeable interaction in which the interaction term Q can change its sign from Q<0 to Q>0 as the universe expands. The evolution trajectories of the statefinder pairs {r,s} and {r,q} are obtained under the circumstance where different values of model parameters are chosen. It is found that the coupling term does not affect the location of the late time attractor, but has an influence on the evolution of the statefinder parameters. Furthermore, it is shown that the evolution trajectories of our model in the r(s) diagram are different from those of other dark energy models.     

Thermodynamical Description of Modified Generalized Chaplygin Gas Model of Dark Energy

We consider a universe filled by a modified generalized Chaplygin gas together with a pressureless dark matter component. We get a thermodynamical interpretation for the modified generalized Chaplygin gas confined to the apparent horizon of FRW universe, whiles dark sectors do not interact with each other. Thereinafter, by taking into account a mutual interaction between the dark sectors of the cosmos, we find a thermodynamical interpretation for interacting modified generalized Chaplygin gas. Additionally, probable relation between the thermal fluctuations of the system and the assumed mutual interaction is investigated. Finally, we show that if one wants to solve the coincidence problem by using this mutual interaction, then the coupling constants of the interaction will be constrained. The corresponding constraint is also addressed. Moreover, the thermodynamic interpretation of using either a generalized Chaplygin gas or a Chaplygin gas to describe dark energy is also addressed throughout the paper.     

Statefinder Diagnostic in Generalized Chaplygin Gas Model with and Without Viscosity

Statefinder diagnostic is a useful method which can distinguish one dark energy model from the others. In this paper, we apply this method to the GCG model with and without viscosity. It is shown that the evolving trajectory of the viscous GCG model in the s–r diagram is not only quite different from the model without viscosity but also different from other dark energy models.     

Dynamical Stability and Attractor of the Variable Generalized Chaplygin Gas Model

For the variable generalized Chaplygin gas （VGCG） as a dynamical system, its stability is analyzed and the related dynamical attractors are investigated. By analysis it is shown that there are two critical points corresponding to the matter-dominated phase and the VGCG dark energy-dominated phase, respectively. Moreover, when the parameters n, a and γ take some fixed values, the phase with ωVGCG = --0.92 is a dynamical attractor and the equation of state of VGCG reaches it from either ωVGCG 〉 --1 or ωVGCG 〈 --1, independent of the initial values of the dynamical system. This shows a satisfactory cosmological model： the early matter-dominated era, followed by the dark energy-dominated era. Meanwhile, the evolutions of density parameters Ωγ and ΩVGCG are quite different from each other. For different initial values of x and y, Ωγ decreases and ωVGCG increases as the time grows, they will eventually approach Ωγ = 0 and ωVGCG ---- 1. Furthermore, since different values of n or a may lead to different equation-of-state parameters ωVGCG, we also discuss the constraints on the parameters n and by the observation data.