scholarly journals BAYESIAN STATISTICS AND PARAMETER CONSTRAINTS ON THE GENERALIZED CHAPLYGIN GAS MODEL USING SNeIa DATA

2005 ◽  
Vol 14 (05) ◽  
pp. 775-796 ◽  
Author(s):  
R. COLISTETE ◽  
J. C. FABRIS ◽  
S. V. B. GONÇALVES
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Hubble Constant ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Accelerating Universe ◽  
Generalized Chaplygin Gas ◽  
Age Of The Universe ◽  
Parameter Constraints ◽  
The Universe

The type Ia supernovae ( SNe Ia ) observational data are used to estimate the parameters of a cosmological model with cold dark matter and the generalized Chaplygin gas model (GCGM). The GCGM depends essentially on five parameters: the Hubble constant, the parameter [Formula: see text] related to the velocity of the sound, the equation of state parameter α, the curvature of the Universe and the fraction density of the generalized Chaplygin gas (or the cold dark matter). The parameter α is allowed to take negative values and to be greater than one. The Bayesian parameter estimation yields [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], where t0 is the age of the Universe and q0 is the value of the deceleration parameter today. Our results indicate that a Universe completely dominated by the generalized Chaplygin gas is favored, which reinforces the idea that the this gas may unify the description for dark matter and dark energy, at least as far as the SNe Ia data is concerned. A closed and accelerating Universe is also favored. The traditional Chaplygin gas model (CGM), α = 1 is not ruled out, even if it does not give the best-fitting. Particular cases with four or three independent free parameters are also analyzed.

scholarly journals TOWARDS CLASSIFICATION OF SIMPLE DARK ENERGY COSMOLOGICAL MODELS

2007 ◽  
Vol 04 (02) ◽  
pp. 313-323 ◽  
Author(s):  
MAREK SZYDLOWSKI ◽  
ALEKSANDRA KUREK
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
Friedmann Equation ◽  
Chaplygin Gas ◽  
Generalized Chaplygin Gas ◽  
Cosmological Time ◽  
Energy Models ◽  
State Formula ◽  
The Universe

We characterize a class of simple FRW models filled by both dark energy and dark matter in notion of a single potential function of the scale factor a(t); t is the cosmological time. It represents the potential of a fictitious particle — Universe moving in 1-dimensional well V(a) which the positional variable mimics the evolution of the Universe. Then the class of all dark energy models (called a multiverse) can be regarded as a Banach space naturally equipped in the structure of the Sobolev metric. In this paper, we explore the notion of C1 metric introduced in the multiverse which measures distance between any two dark energy models. If we choose cold dark matter as a reference, then we can find how far apart are different models offering explanation of the present accelerating expansion phase of the Universe. We consider both models with dark energy (models with the generalized Chaplygin gas, models with variable coefficient equation of state [Formula: see text] parameterized by redshift z, models with phantom matter) as well as models based on some modification of Friedmann equation (Cardassian models, Dvali–Gabadadze–Porrati brane models). We argue that because observational data still favor the ΛCDM model, all reasonable dark energy models should belong to the nearby neighborhood of this model.

THE GENERALIZED CHAPLYGIN GAS MODEL WITH INTERACTION

2007 ◽  
Vol 16 (10) ◽  
pp. 1601-1609 ◽  
Author(s):  
YABO WU ◽  
SONG LI ◽  
HAI YANG ZHONG ◽  
LEI LI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Generalized Chaplygin Gas ◽  
Phantom Divide ◽  
Big Rip ◽  
The Future ◽  
Two Fluid

A two-fluid generalized Chaplygin gas (GCG) model including two different cases is considered in this paper. Concretely, the evolution of the GCG model with interaction is discussed and the statefinder diagnostic for the GCG models is performed, respectively. By analysis, we show that the effective state parameter of dark energy can cross the so-called phantom divide ω = -1, the behavior of GCG will be like ΛCDM in the future and therefore our Universe will not end up with the Big Rip in the future. In addition, we find that the statefinder diagnostic can differentiate the GCG model with or without interaction. Also, trajectories of both the GCG model mixed with cold dark matter (CDM) and the pure GCG model in the parameter plane are illustrated to be significantly different.

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.

Friedmann–Robertson–Walker (FRW) cosmological model in the present perspective

2019 ◽  
Vol 97 (6) ◽  
pp. 588-595 ◽  
Author(s):  
G.K. Goswami
Keyword(s):  
Cosmological Model ◽  
Perfect Fluid ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
State Parameter ◽  
Accelerating Universe ◽  
Frw Cosmological Model ◽  
The Universe ◽  
Friedmann Robertson Walker

In this paper, we have presented a cosmological model that represents spatially homogenous and isotropic accelerating universe from the perspective of the latest developments begun by Perlmutter and Riess in cosmology. For this, Friedmann–Robertson–Walker (FRW) space–time metric is considered and our universe is assumed to be filled with two types of fluids. One is ordinary baryonic perfect fluid and the other one is mysterious and bizarre dark energy perfect fluid with negative pressure. This creates a repulsive field that produces acceleration in the universe. We have used 581 Union 2.1 compilation data to statistically estimate present values of cosmological parameters Ωde, Ωm, Ωk and equation of state parameter ωde for our model. We have used 31 datasets of observed values of Hubble constant for various redshifts to estimate the present value of Hubble constant H0. On the basis of these we have calculated the present age of the universe, densities, and deceleration parameter. Evolution of deceleration parameter shows that our universe has gone through an accelerating phase two times. In the beginning, and at present. We have also calculated Particle horizon and the time at which acceleration began. Our results are close to latest surveys.

scholarly journals The Hubble Constant

2000 ◽  
Vol 17 (1) ◽  
pp. 45-47 ◽  
Author(s):  
Jeremy Mould
Keyword(s):  
Globular Clusters ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Big Bang ◽  
Accelerating Universe ◽  
De Sitter ◽  
Age Of The Universe ◽  
Extragalactic Distance Scale ◽  
The Big Bang ◽  
The Universe

AbstractWith the completion of the Hubble Space Telescope (HST) Key Project on the Extragalactic Distance Scale, it is interesting to form the dimensionless quantity H0t0 by multiplying the Hubble Constant by the age of the Universe. In a matter dominated decelerating Universe with a density exceeding 0·26 of the critical value, H0t0 < 1; in an accelerating Universe with the same Ωm = 0·26, but dominated by vacuum energy with ΩV ≥ 1 – Ωm, H0t0 ≥ 1. If the first globular clusters formed 109 years after the Big Bang, then with 95% confidence H0t0 =1·0 ± 0·3. The classical Einstein–de Sitter cosmological model has H0t0 = ⅔.

scholarly journals BAYESIAN ANALYSIS OF THE CHAPLYGIN GAS AND COSMOLOGICAL CONSTANT MODELS USING THE SNe Ia DATA

2004 ◽  
Vol 13 (04) ◽  
pp. 669-693 ◽  
Author(s):  
R. COLISTETE ◽  
J. C. FABRIS ◽  
S. V. B. GONÇALVES ◽  
P. E. DE SOUZA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Confidence Level ◽  
Cold Dark Matter ◽  
Chaplygin Gas ◽  
Type Ia Supernovae ◽  
Λcdm Model ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe

The type Ia supernovae observational data are used to estimate the parameters of a cosmological model with cold dark matter and the Chaplygin gas. This exotic gas, which is characterized by a negative pressure varying with the inverse of density, represents in this model the dark energy responsible for the acceleration of the Universe. The Chaplygin gas model depends essentially on four parameters: the Hubble constant, the velocity of the sound of the Chaplygin gas, the curvature of the Universe and the fraction density of the Chaplygin gas and the cold dark matter. The Bayesian parameter estimation yields [Formula: see text] and [Formula: see text]. These and other results indicate that a Universe completely dominated by the Chaplygin gas is favoured, what reinforces the idea that the Chaplygin gas may unify the description for dark matter and dark energy, at least as the type Ia supernovae data are concerned. A closed and accelerating Universe is also favoured. The Bayesian statistics indicates that the Chaplygin gas model is more likely than the standard cosmological constant (ΛCDM) model at 55.3% confidence level when an integration on all free parameters is performed. Assuming the spatially flat curvature, this percentage mounts to 65.3%. On the other hand, if the density of dark matter is fixed at zero value, the Chaplygin gas model becomes more preferred than the ΛCDM model at 91.8% confidence level. Finally, the hypothesis of flat Universe and baryonic matter (Ωb0=0.04) implies a Chaplygin gas model preferred over the ΛCDM at a confidence level of 99.4%.

scholarly journals Viscous interacting and stability on dark matter Bose-Einstein condensation with modified Chaplygin gas

2021 ◽  
Author(s):  
E. Mahichi ◽  
Alireza Amani ◽  
M.A. Ramzanpour
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
Einstein Condensation ◽  
Modified Chaplygin Gas ◽  
Bose Einstein Condensation ◽  
Bose Einstein ◽  
The Universe

In this paper, the viscous cosmological dynamics are studied in the presence of dark matter Bose-Einstein Condensation (BEC) by curved-FRW background. For this purpose, we use the BEC regime rather than the normal dark matter (the cold dark matter or the barotropic dark matter) with the dark matter Equation of State (EoS) as p<sub>dm </sub>∝ p<sup>2</sup><sub>dm</sub>, which arises from the gravitational form. Therefore, we obtain the corresponding continuity equations with the existence of the universe components by considering an interacting model with modified Chaplygin gas. Afterward, we derive the energy density and the pressure of dark energy in terms of the redshift parameter. And then, by introducing a parametrization function and fitting it with 51 supernova data with the likelihood analysis, we find the cosmological parameters versus redshift parameter. In what follows, we plot the corresponding dynamic graphs proportional to redshift, and then we represent the universe is currently undergoing an accelerated expansion phase. Finally, we explore the stability and the instability of the present model with the sound speed parameter.

scholarly journals The Hot Big Bang and Beyond

1996 ◽  
Vol 168 ◽  
pp. 301-320
Author(s):  
Michael S. Turner
Keyword(s):  
Dark Matter ◽  
Cold Dark Matter ◽  
Hubble Space Telescope ◽  
Hubble Constant ◽  
Big Bang ◽  
Small Admixture ◽  
Matter Theory ◽  
Density Perturbations ◽  
The Big Bang ◽  
The Universe

The hot big-bang cosmology provides a reliable accounting of the Universe from about 10−2sec after the bang until the present, as well as a robust framework for speculating back to times as early as 10−43sec. Cosmology faces a number of important challenges; foremost among them are determining the quantity and composition of matter in the Universe and developing a detailed and coherent picture of how structure (galaxies, clusters of galaxies, superclusters, voids, great walls, and so on) developed. At present there is a working hypothesis—cold dark matter—which is based upon inflation and which, if correct, would extend the big bang model back to 10−32sec and cast important light on the unification of the forces. Many experiments and observations, from CBR anisotropy experiments to Hubble Space Telescope observations to experiments at Fermilab and CERN, are now putting the cold dark matter theory to the test. At present it appears that the theory is viable only if the Hubble constant is smaller than current measurements indicate (around 30 km s−1Mpc−1), or if the theory is modified slightly, e.g., by the addition of a cosmological constant, a small admixture of hot dark matter (5 eV “worth of neutrinos”), more relativistic particles, or a tilted spectrum of density perturbations.

Ω0 Concordance

2005 ◽  
Vol 201 ◽  
pp. 271-281
Author(s):  
Masataka. Fukugita
Keyword(s):  
Dark Matter ◽  
Cosmological Constant ◽  
Structure Formation ◽  
Cold Dark Matter ◽  
Mass Density ◽  
Hubble Constant ◽  
Density Parameter ◽  
Microwave Background ◽  
The Hierarchical Structure ◽  
The Universe

The determinations of the mass density parameter Ω0 are examined with a particular emphasis given to the new cosmic microwave background (CMB) experiments. It is shown that the Ω0 and the Hubble constant H0 from CMB are quite consistent with those from other observations with the aid of the hierarchical structure formation models based on cold dark matter dominance with the cosmological constant that makes the universe flat. The concordance value of Ω0 is 0.25-0.45.

THE EVOLUTION OF GENERALIZED CHAPLYGIN GAS

2006 ◽  
Vol 21 (15) ◽  
pp. 1233-1239 ◽  
Author(s):  
YABO WU ◽  
XUEMEI DENG ◽  
JIANBO LU ◽  
SONG LI ◽  
XIUYI YANG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Critical Density ◽  
Chaplygin Gas ◽  
Generalized Chaplygin Gas ◽  
Big Rip ◽  
The Future ◽  
The Universe

We consider the generalized Chaplygin gas (GCG) proposal for the unification of dark matter and dark energy with p = pdeand ρ = ρdm+ρde. The unified equation of state for GCG has been obtained: [Formula: see text]. On the basis of the function χ(z), 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 equation of state for dark energy ωde, the deceleration parameter q are all obtained, which are consistent with observations. In addition, the transition from deceleration to acceleration is described in our model. We find that the behavior of GCG will be like ΛCDM in the future. So, it has been ruled out in our model that our universe will end up with Big Rip in the future.

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