VISCOUS GENERALIZED CHAPLYGIN GAS

2006 ◽  
Vol 15 (08) ◽  
pp. 1151-1161 ◽  
Author(s):  
XIANG-HUA ZHAI ◽  
YOU-DONG XU ◽  
XIN-ZHOU LI
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Critical Energy ◽  
State Equation ◽  
Chaplygin Gas ◽  
Point Of View ◽  
Dynamical Analysis ◽  
Density Parameter ◽  
Generalized Chaplygin Gas ◽  
Barotropic Fluid

Viscous generalized Chaplygin gas (GCG) cosmology is discussed, assuming that there is bulk viscosity in the linear barotropic fluid and GCG. wγ = γ - 1 and wg represent the state equation parameters for barotropic fluid and GCG, respectively, in which γ = 1 or [Formula: see text] corresponds to ordinary matter or radiation. The dynamical analysis indicates that the phase [Formula: see text] is a dynamical attractor and the equation of state of GCG approaches it from either wg > -1 or wg < -1 depending on the choice of its initial cosmic density parameter and the ratio of pressure to critical energy density, where τg and τγ are viscosity parameters. Therefore, the equation of state wg will cross the boundary wg = -1 if we choose initial value wg < -1. Furthermore, we show that bulk viscosity coefficients should satisfy inequalities from the point of view of dynamics.

scholarly journals The universe dominated by the extended Chaplygin gas

2015 ◽  
Vol 30 (13) ◽  
pp. 1550070 ◽  
Author(s):  
E. O. Kahya ◽  
B. Pourhassan
Keyword(s):  
Phase Transition ◽  
Equation Of State ◽  
Critical Point ◽  
Order Term ◽  
Chaplygin Gas ◽  
Point Of View ◽  
Fluid Equation ◽  
Barotropic Fluid ◽  
Density Perturbations ◽  
The Universe

In this paper, we consider a universe dominated by the extended Chaplygin gas which was recently proposed as the last version of Chaplygin gas models. Here, we only consider the second-order term which recovers quadratic barotropic fluid equation of state. The density perturbations are analyzed in both relativistic and Newtonian regimes and show that the model is stable without any phase transition and critical point. We confirmed stability of the model using thermodynamics point of view.

scholarly journals GEOMETRICAL DIAGNOSTIC FOR THE GENERALIZED CHAPLYGIN GAS MODEL

2009 ◽  
Vol 18 (11) ◽  
pp. 1741-1748 ◽  
Author(s):  
JIANBO LU ◽  
LIXIN XU
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Diagnostic Method ◽  
Chaplygin Gas ◽  
Shift Parameter ◽  
Generalized Chaplygin Gas ◽  
Λcdm Model ◽  
Current Equation

A new diagnostic method, Om, is applied to the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy. On the basis of the recently observed data — the Union supernovae, the observational Hubble data, the SDSS baryon acoustic peak and the five-year WMAP shift parameter — we show the discriminations between the GCG model and the ΛCDM model. Furthermore, it is calculated that the current equation of state of dark energy w 0de = -0.964, according to the GCG model.

Stability of a charged rotating BTZ thin shell with a different variable equation of state

2021 ◽  
pp. 2150086
Author(s):  
A. Eid
Keyword(s):  
Black Holes ◽  
Equation Of State ◽  
Thin Shell ◽  
Mechanical Stability ◽  
Chaplygin Gas ◽  
Throat Radius ◽  
Generalized Chaplygin Gas ◽  
Radial Perturbation ◽  
Btz Black Holes ◽  
Variable Equation

Dynamics of charged rotating BTZ black holes in 2 + 1 dimensions by using the cut and paste approach is discussed. Due to the mechanical stability of rotating charged BTZ thin shell, the radial perturbation about the equilibrium throat radius and three variable equation of state (EoS) is analyzed. Several examples are displayed satisfying it, such as variable Phantom-like, variable Chaplygin gas and variable modified generalized Chaplygin gas.

scholarly journals Spherical "Top-Hat" collapse in a modified Chaplygin gas dominated universe

2015 ◽  
Vol 24 (07) ◽  
pp. 1550050 ◽  
Author(s):  
S. Karbasi ◽  
H. Razmi
Keyword(s):  
Equation Of State ◽  
Structure Formation ◽  
Observational Data ◽  
Chaplygin Gas ◽  
Modified Chaplygin Gas ◽  
Time Rate ◽  
Generalized Chaplygin Gas ◽  
The Stability ◽  
Perturbation Growth ◽  
Good Agreement

Considering perturbation growth in spherical Top-Hat (STH) model of structure formation in a generalized Chaplygin gas (GCG) dominated universe, we want to study this scenario with modified Chaplygin gas (MCG) obeying an equation of state p = A - B/ρα model. Different parameters of this scenario for positive and negative values of A are computed. The evolution of background and collapsed region parameters are found for different cases. The stability of the model and the collapse time rate are considered in different cases. The turn-around redshifts for different values of α are computed; the results are in relatively good agreement with current observational data.

Dark energy and viscous cosmology with variable G and Λ in an anisotropic background

2013 ◽  
Vol 91 (2) ◽  
pp. 153-157 ◽  
Author(s):  
V. Fayaz ◽  
M.R. Setare ◽  
H. Hossienkhani
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Bulk Viscosity ◽  
Deceleration Parameter ◽  
Chaplygin Gas ◽  
Density Parameter ◽  
Type I ◽  
De Sitter ◽  
Variable G And Λ ◽  
Variable G

The general Bianchi type I with dark energy in the form of standard and modified Chaplygin gas with variable G and Λ and bulk viscosity have been investigated. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models that reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe, that which yields a constant value for the deceleration parameter. We reconstruct bulk viscosity, ξ, gravitational parameter, G, cosmological term, Λ, density parameter, Ω, cosmological constant density parameter, ΩΛ, and deceleration parameter, q, for different equations of state. In the large time limit the model describes an accelerating universe wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.

scholarly journals Viscous generalized Chaplygin gas interacting with f(R,T) gravity

2017 ◽  
Vol 14 (04) ◽  
pp. 1750051 ◽  
Author(s):  
E. H. Baffou ◽  
M. J. S. Houndjo ◽  
I. G. Salako
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Graphical Representation ◽  
Input Parameter ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Generalized Chaplygin Gas ◽  
Accelerating Expansion

In this paper, we study in Friedmann–Robertson–Walker universe the interaction between the viscous generalized Chaplygin gas with [Formula: see text] gravity, which is an arbitrary function of the Ricci scalar [Formula: see text] and the trace [Formula: see text] of the energy–momentum tensor. Assuming that the contents of universe are dominated by a generalized Chaplygin gas and dark energy, we obtained the modified Friedmann equations and also the time-dependent energy density and pressure of dark energy due to the shear and bulk viscosities for three interacting models depending on an input parameter [Formula: see text]. Within the simple form of scale factor (power-law), we discuss the graphical representation of dark energy density parameter and investigate the shear and bulk viscosities effects on the accelerating expansion of the universe for each interacting model.

scholarly journals Study of thermal stability for different dark energy models

2019 ◽  
Vol 16 (11) ◽  
pp. 1950171
Author(s):  
Abdulla Al Mamon ◽  
Pritikana Bhandari ◽  
Subenoy Chakraborty
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Point Of View ◽  
Frw Universe ◽  
Generalized Chaplygin Gas ◽  
Dark Fluid ◽  
Energy Models

In this work, we have made an attempt to investigate the dark energy possibility from the thermodynamical point of view. For this purpose, we have studied thermodynamic stability of three popular dark energy models in the framework of an expanding, homogeneous, isotropic and spatially flat FRW Universe filled with dark energy and cold dark matter. The models considered in this work are Chevallier–Polarski–Linder (CPL) model, Generalized Chaplygin Gas (GCG) model and Modified Chaplygin Gas (MCG) model. By considering the cosmic components (dark energy and cold dark matter) as perfect fluid, we have examined the constraints imposed on the total equation of state parameter ([Formula: see text]) of the dark fluid by thermodynamics and found that the phantom nature ([Formula: see text]) is not thermodynamically stable. Our investigation indicates that the dark fluid models (CPL, GCG and MCG) are thermodynamically stable under some restrictions of the parameters of each model.

scholarly journals Interacting models of generalized Chaplygin gas and modified Chaplygin gas with barotropic fluid

2019 ◽  
Vol 34 (09) ◽  
pp. 1950064 ◽  
Author(s):  
Promila Biswas ◽  
Ritabrata Biswas
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Cosmological Parameters ◽  
Chaplygin Gas ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Modified Chaplygin Gas ◽  
Interaction Coefficients ◽  
Generalized Chaplygin Gas ◽  
Barotropic Fluid

In this paper, we consider two different models of our present universe. We choose the models which consist of different sets of two separate fluids. The first one of each set tries to justify the late time acceleration and the second one is barotropic fluid. The former model considers our present time universe to be homogeneously filled up by Generalized Chaplygin Gas which is interacting with barotropic fluid. On the other hand, the latter model considers that the cosmic acceleration is generated by Modified Chaplygin Gas which is interacting with matter depicted by barotropic equation of state (EoS). For both the models, we consider the interaction term to vary proportionally with Hubble’s parameter as well as with the exotic matter/dark energy’s energy density. We find an explicit function form of the energy density of the cosmos which is found to depend on different cosmological parameters like scale factor, dark energy and barotropic fluid’s EoS parameters and other constants, like interacting constants, etc. We draw curves of effective EoS-s, different cosmological parameters like deceleration parameter q, statefinder parameters r and s with respect to the redshift z (for different values of dark energy and barotropic fluid parameters) and study them thoroughly. We compare two models as well as the nature of dependencies on these models’ interaction coefficients. We point out the particular redshift for which the universe may transit from a deceleration to acceleration phase. We tally all these values with different observational data. Here, we also analyze how this value of particular redshift does change for different values of interaction coefficients and different dark energy models.

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