Generalized Chaplygin Gas Model Research Articles

Constraining the variable generalized Chaplygin gas model in matter creation cosmology

We explore the variable generalized Chaplygin gas (VGCG) model in the theory of matter creation cosmology within the framework of a spatially homogeneous and isotropic flat Friedmann—Lemaître—Robertson—Walker space-time. Matter creation cosmology is based on reinterpretation of the energy–momentum tensor in Einstein’s field equations. This creation corresponds to an irreversible energy flow from the gravitational field to the created matter constituents. The variable Chaplygin gas (VCG) is also studied as a particular solution. We use the Markov chain Monte Carlo method to constrain the free parameters of three models, namely, Lambda-Cold-Dark matter (ΛCDM), VGCG and VCG models with and without matter creation from the latest observational data from baryon acoustic oscillations, cosmic chronometer, type Ia supernovae (Pantheon) including gamma-ray bursts, quasars and the local measurement of H 0 from R21 data. Two different combinations of dataset provide a fairly tight constraint on the parameters of the ΛCDM, VGCG and VCG models. The present values of various cosmological parameters are obtained, which are very close to the ΛCDM model. Furthermore, we perform stability analysis, Bayesian evidence analysis and information criteria analysis for these models through studying the sound speed, Bayes factor, and Akaike information criteria (AIC) and Bayesian information criteria (BIC) selection criteria. The values of sound speed for VGCG and VCG models shows that both the models are stable. According to AIC, it is observed that VGCG and VCG models with matter creation are supported considerably less by current observations, while BIC shows that these models are not favoured by observational data.

Stability of lower dimensional counter-rotating thin-shell wormholes with scalar hair

The motivation for constructing a thin-shell wormhole from a (2+1)-dimensional rotating black hole arises from the desire to study the effects of a nonminimally coupled scalar field in this particular spacetime. By investigating the behavior of such a field in the presence of rotation, we can gain insights into the interplay between gravity and scalar fields in lower-dimensional systems. Additionally, this construction allows us to explore potential connections between black hole physics and exotic phenomena like traversable wormholes. The radial perturbation around the equilibrium throat radius is considered to explore the stable configuration for specific values of physical parameters. Then, the equations of state, specifically the phantom-like and generalized Chaplygin gas model for exotic matter is used to conduct an extensive investigation into the stability of the counter-rotating thin-shell wormholes. Our results show that the presence of a scalar field enhances the stability of the counter-rotating thin-shell wormholes.

On Chaplygin models in f(G) gravity

This work treats cosmological perturbation in a mixture of standard matter, Chaplygin gas as well as Gauss–Bonnet fluids using a 1+3 covariant approach in the context of modified [Formula: see text] gravity. We define the gradient variables to obtain linear perturbation equations. After scalar and redshift transformations, we consider both an original Chaplygin and generalized Chaplygin gas models under Gauss–Bonnet gravity. For pedagogical purposes, the consideration of polynomial [Formula: see text] gravity model was used to solve the perturbation equations for short- and long-wavelength modes and investigate the late-time evolution. The numerical solutions were obtained. The results show that the energy overdensity perturbations decay with an increase in redshift. The treatment recovers GR results under limiting cases.

Viscous generalized Chaplygin gas model in Brans–Dicke theory

The Kantowski–Sachs cosmological model for viscous generalized Chaplygin gas has been investigated in the Brans–Dicke theory of gravitation. To determine the solutions of field equations, we have considered the power-law relation for the average scale factor. We have computed some cosmological parameters and discussed their physical importance. Furthermore, we have discussed the nature of statefinder and [Formula: see text] diagnostics in our model. It is also worth noting that the conclusions of the cosmological parameter are consistent with modern observational data.

Growth of fluctuations in Chaplygin gas cosmologies: A nonlinear Jeans scale for unified dark matter

Unified dark matter cosmologies economically combine missing matter and energy in a single fluid. Of these models, the standard Chaplygin gas is theoretically motivated, but faces problems in explaining large scale structure if linear perturbations are directly imposed on the homogeneous fluid. However, early formation of a clustered component of small halos is sufficient (and necessary) for hierarchical clustering to proceed in a cold dark matter (CDM) component as in the standard scenario, with the remaining homogeneous component acting as dark energy. We examine this possibility. A linear analysis shows that a critical Press-Schechter threshold for collapse can generally only be reached for generalized Chaplygin gas models that mimic $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, or ones where superluminal sound speeds occur. However, the standard Chaplygin gas case turns out to be marginal, with overdensities reaching order one in the linear regime. This motivates a nonlinear analysis. A simple infall model suggests that collapse is indeed possible for perturbations of order 1 kpc and above; for, as opposed to standard gases, pressure forces decrease with increasing densities, allowing for the collapse of linearly stable systems. This suggests that a cosmological scenario based on the standard Chaplygin gas may not be ruled out from the viewpoint of structure formation, as often assumed. On the other hand, a ``nonlinear Jeans scale,'' constricting growth to scales $R\ensuremath{\gtrsim}\mathrm{kpc}$, which may be relevant to the small scale problems of CDM, is predicted. Finally, the background dynamics of clustered Chaplygin gas cosmologies is examined and confronted with observational datasets. It is found to be viable (at 1-sigma), with a mildly larger ${H}_{0}$ than $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, if the clustered fraction is larger than 90%.

Reconstruction of [formula omitted] gravity in homogeneous backgrounds and a general prescription for reconstructing through scalar field

A technique for the reconstruction of the potential for a scalar field in cosmological models based on induced gravity has recently been developed by Alexander Y. Kamenshchik, Alessandro Tronconi, and Giovanni Venturi (Kamenshchik et al., 2011). In this paper, this extended reconstruction method is utilized to investigate the nature of the scalar potentials of the most extended action of F(T)-gravity context. First, a general formalism is formulated and then it is utilized for considering some well-known special cases including ‘Barotropic Fluid’, ‘Cosmological Constant’, and ‘Modified Chaplygin Gas’.The analysis of the results is carried out by the use of the B-function method which has recently been suggested by the author (Tajahmad, 2020).As we know, assuming a proportional relation between the scale factor of the x-direction and the scale factors of y and z directions (i.e. A=Bm) in dealing with LRS Bianchi-I background is prevalent. Pursuant to observational data, the correct physical range of m is extracted. It is demonstrated that, unlike several papers, m is very close to 1.Some interesting discussions about the modified and generalized Chaplygin gases are performed. The ranges of the amounts of free parameters of the various types of Chaplygin gases are corrected according to observational data. It is demonstrated that the generalized Chaplygin gas model namely P=−σ2/ρν may be developed as P=−σ2/ρν(t) (i.e. ν=const.⟶ν=ν(t)).Ultimately, by combining Ref. Kamenshchik et al. (2011) and the current paper, a general prescription is recommended for the reconstruction of the potentials of alternative theories of gravity (especially F(φ)R and F(T)), and their relevant analysis. Furthermore, a recurring scheme of the analysis of the results is presented for the clarification.

Generalized Chaplygin gas and accelerating universe in f(Q,T) gravity

The generalized Chaplygin gas (GCG), which has an unusual perfect fluid equation of state, is another promising candidate for dark energy. We investigate the GCG scenario coupled with a baryonic matter in a newly suggested $f(Q,T)$ gravity, an arbitrary function of non-metricity $Q$ and the trace of energy-momentum tensor $T$. We consider the functional form of $f(Q, T)$ as a linear combination of $Q$ and an arbitrary function of $T$, denoted by $h(T)$. Furthermore, we obtain two different functional forms of the $f(Q,T)$ model under high pressure and high-density scenarios of GCG. We also test each model with the recent Pantheon supernovae data set of 1048 data points, Hubble data set of 31 points, and baryon acoustic oscillations. The deceleration parameter is constructed using $OHD+SNeIa+BAO$, predicting a transition from decelerated to accelerated phases of the universe expansion. Also, the equation of state parameter acquires a negative behavior depicting acceleration. Finally, we analyze the statefinder diagnostic to discriminate between the GCG and other dark energy models.

Revisiting Chaplygin gas cosmologies with the recent observations of high-redshift quasars

In this paper, we use the latest observations of quasars covering the redshift range of 0.04<z<5.1 to investigate a series of Chaplygin gas models as candidates for unified dark matter and dark energy. Based on different combinations of available standard candle and standard ruler data, we put constraints on the generalized Chaplygin gas (GCG), modified Chaplygin gas (MCG), new generalized Chaplygin gas (NGCG) and viscous generalized Chaplygin gas (VGCG) models. Moreover, we apply Jensen–Shannon divergence (JSD), statefinder diagnostics, and the deviance information criterion (DIC) to distinguish these CG models, based on the statistical results derived from Markov chain Monte Carlo method. The results show that (1) The standard ruler data could provide more stringent constraints on the cosmological parameters of different CG models considered in this analysis. Interestingly, the matter density parameter varOmega _{m} and Hubble constant H_{0} derived from the available data are well consistent with those from the Planck 2018 results; (2) Based on the statistical criteria JSD, our findings demonstrate the well consistency between Chaplygin gas and the concordance varLambda CDM model. However, in the framework of statefinder diagnostics, the GCG and NGCG models cannot be distinguished from varLambda CDM, while MCG and VGCG models show significant deviation from varLambda CDM in the present epoch; (3) According to the the statistical criteria DIC, we show that the MCG and VGCG models have substantial observational support from high-redshift quasars, whereas the GCG and NGCG models miss out on the less observational support category but can not be ruled out.

New parameterizations of generalized Chaplygin gas model constrained at background and perturbation levels

We study the main cosmological properties of the generalized Chaplygin gas (GCG) dark energy model at the background and perturbation levels. By using the latest cosmological data in both the background and perturbation levels, we implement a joint likelihood analysis to constrain the cosmological parameters of the model. Using the available expansion and growth rate data, we place constraints on the free parameters of the GCG model based on the statistical Markov chain Monte Carlo method. Then, the best-fit values of cosmological parameters and those of confidence regions are found. We obtain the best-fit value of the current expansion rate of the Universe in the GCG model and show that it is in good agreement with the $$\Lambda$$ CDM model. Moreover, the growth rate of matter perturbations is investigated in the context of a unified GCG model. It is shown that in this model, the dark energy component, like the $$\Lambda$$ sector in the $$\Lambda$$ CDM model, can suppress the amplitude of matter perturbations. We show that the growth rate of perturbations in GCG parametrization is consistent with cluster-scale observations similar to the case of the concordance $$\Lambda$$ CDM model. Our results show that the tension on $$\sigma _{8}$$ appeared in the concordance model can be alleviated in GCG cosmology.

An extended analysis for a generalized Chaplygin gas model

In this work, we have extended the analysis on the generalized Chaplygin gas (GCG) model as the unification of dark energy and dark matter. Specifically, we have shown that the model of our consideration known as the new generalized Chaplygin gas (NGCG) model, admits a scalar field description, which means that there exist a minimally coupled scalar field for a given scalar field potential where the equation of state is that of the NGCG. With the use of the later property we can construct the slow-roll parameters and derive the corresponding values for the spectral indices for the tensor to scalar perturbation and for the density perturbations. We have also studied the growth rate of matter perturbations in the NGCG scenario. Finally, we have studied the viability of the generalized second law of thermodynamics by assuming that the dynamical apparent horizon in a NGCG universe is endowed with Hawking temperature and Bekenstein entropy.

Statefinder and Om Diagnostics for New Generalized Chaplygin Gas Model

We explore a unified model of dark matter and dark energy. This new model is a generalization of the generalized Chaplygin gas model and is known as a new generalized Chaplygin gas (NGCG) model. We study the evolutions of the Hubble parameter and the distance modulus for the model under consideration and the standard ΛCDM model and compare that with the observational datasets. Furthermore, we demonstrate two geometric diagnostics analyses including the statefinder (r,s) and Om(z) to the discriminant NGCG model from the standard ΛCDM model. The trajectories of evolution for (r,s) and Om(z) diagnostic planes are shown to understand the geometrical behavior of the NGCG model by using different observational data points.

Noncommutative-Geometry Wormholes with Isotropic Pressure

The strategy adopted in the original Morris-Thorne wormhole was to retain complete control over the geometry at the expense of certain engineering considerations. The purpose of this paper is to obtain several complete wormhole solutions by assuming a noncommutative-geometry background with a concomitant isotropic pressure condition. This condition allows us to consider a cosmological setting with a perfect-fluid equation of state. An extended form of the equation generalizes the first solution and subsequently leads to the generalized Chaplygin gas model and hence to a third solution. The solutions obtained extend several previous results. This paper also reiterates the need for a noncommutative-geometry background to account for the enormous radial tension that is a characteristic of Morris-Thorne wormholes.

Varying alpha generalized Dirac-Born-Infeld models

We study the cosmological consequences of a class of Dirac-Born-Infeld models, and assess their viability as a candidate for the recent acceleration of the Universe. The model includes both the rolling tachyon field and the generalized Chaplygin gas models as particular limits, and phenomenologically each of these provides a possible mechanism for a deviation of the value of the dark energy equation of state from its canonical (cosmological constant) value. The field-dependent potential that is characteristic of the rolling tachyon also leads to variations of the fine-structure constant $\alpha$, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of $\alpha$. Our analysis, using the latest available low-redshfit data and local constraints from atomic clock and weak equivalence principle experiments, shows that the two possible deviations of the dark energy equation of state are constrained to be $\log_{10}{(1+w_0)_V}<-7.85$ and $\log_{10}{(1+w_0)_C}<-0.85$, respectively for the rolling tachyon and Chaplygin components, both being at the $95.4\%$ confidence level (although the latter depends on the choice of priors, in a way that we quantify). Alternatively, the $95.4\%$ confidence level bound on the dimensionless slope of the potential is $\log_{10}{\lambda}<-5.36$. This confirms previous analyses indicating that in these models the potential needs to be extremely flat.

No slow-roll inflation à la generalized Chaplygin gas in general relativity

The Generalized Chaplygin Gas (GCG) model is characterized by the equation of state P = −A ρ−α, where A>0 and α < 1. The model has been extensively studied due to its interesting properties and applicability in several contexts, from late-time acceleration to primordial inflation. Nonetheless we show that the inflationary slow-roll regime cannot be satisfied by most of the parameter space of the GCG model when General Relativity (GR) is considered. In particular, although the model has been applied to inflation with 0 < α < 1, we show that for −1 < α ≤ 1 there is no expansion of the Universe but an accelerated contraction. For α ≤ −5/3, the second slow-roll parameter ηH is larger than unity, so there is no sustained period of inflation. Only for α very close to -1 the model produces enough e-folds, thus greatly reducing its parameter space. Moreover, we show that the model is ruled out by the Planck 2018 results. Finally, we extend our analysis to the Generalized Chaplygin-Jacobi Gas (GCJG) model. We find that the introduction of a new parameter does not change the previous results. We thus conclude that the violation of the slow-roll conditions is a generic feature of the GCG and GCJG models during inflation when GR is considered and that the models are ruled out by the Planck 2018 results.

Cosmological constrains on new generalized Chaplygin gas model

We use different combinations of data samples to investigate the new generalized Chaplygin gas (NGCG) model in the context of dark energy (DE) cosmology. Using the available cosmological data, we put constraints on the the free parameters of NGCG model based on the statistical Markov chain Monte Carlo method. We then find the best fit values of cosmological parameters and those confidence regions in NGCG cosmology. Our result for the matter density parameter calculated in NGCG model is in excellent agreement with that of the standard $$\Lambda $$ CDM cosmology. We also find that the equation of state of DE of the model slightly favors the phantom regime. We show that the big tension between the low- and high-redshift observations appearing in $$\Lambda $$ CDM universe to predict the Hubble constant $$H_0$$ can be alleviated in NGCG model. However, from the statistical point of view, our results show that the standard $$\Lambda $$ CDM model fits the observations better than the NGCG cosmology.

Dawn of the dark: unified dark sectors and the EDGES Cosmic Dawn 21-cm signal

While the origin and composition of dark matter and dark energy remains unknown, it is possible that they might represent two manifestations of a single entity, as occurring in unified dark sector models. On the other hand, advances in our understanding of the dark sector of the Universe might arise from Cosmic Dawn, the epoch when the first stars formed. In particular, the first detection of the global 21-cm absorption signal at Cosmic Dawn from the EDGES experiment opens up a new arena wherein to test models of dark matter and dark energy. Here, we consider generalized and modified Chaplygin gas models as candidate unified dark sector models. We first constrain these models against Cosmic Microwave Background data from the Planck satellite, before exploring how the inclusion of the global 21-cm signal measured by EDGES can improve limits on the model parameters, finding that the uncertainties on the parameters of the Chaplygin gas models can be reduced by a factor between 1.5 and 10. We also find that within the generalized Chaplygin gas model, the tension between the CMB and local determinations of the Hubble constant H0 is reduced from ≈ 4σ to ≈ 1.3σ. In conclusion, we find that the global 21-cm signal at Cosmic Dawn can provide an extraordinary window onto the physics of unified dark sectors.

Constraining Chaplygin models using diffuse supernova neutrino background

In this work, we examine the possibility of using the diffuse supernova neutrino background (DSNB) to test the Chaplygin gas (CG) models of the Universe. With a typical supernova rate $R_{\mathrm{SN}}(z)$ and supernova neutrino spectrum $\mathrm{d} N(E_\nu)/\mathrm{d} E_\nu$, the DSNB flux spectrum $n(E_\nu)$ in three categories of CG models, the generalized CG (GCG), modified CG (MCG) and extended CG (ECG) models, are studied. It is found that generally the flux spectra take a form similar to a Fermi-Dirac distribution with a peak centered around 3.80-3.97 MeV. The spectrum shape and peak positions are primarily determined by $R_{\mathrm{SN}}(z)$ and $\mathrm{d} N(E_\nu)/\mathrm{d} E_\nu$ and only slightly affected by the CG models. However, the height of the spectra in each category of the CG models can vary dramatically for different models, with variances of 13.2%, 23.6% and 14.9% for GCG, MCG and ECG categories respectively. The averaged total flux in each category are also different, with the ECG model average 10.0% and 12.7% higher than that of the GCG and MCG models. These suggest that the DSNB flux spectrum height and total flux can be used to constrain the CG model parameters, and if the measured to a sub-10% accuracy, might be used to rule out some models.

Linearized stability of Bardeen anti-de Sitter wormholes

In this paper, we explore the stable and unstable geometrical structures of thin-shell wormholes. We use Visser cut and paste approach to develop thin-shell from Bardeen anti-de Sitter black holes. The characteristics of matter distribution are determined by using Israel formalism. We discuss the existence of exotic matter at the wormhole throat through energy conditions and examine the attractive/repulsive nature of wormhole throat. The linearized stability of thin-shell is studied through barotropic and variable equations of state (generalized phantomlike and generalized Chaplygin gas model). We conclude that the stability of wormhole depends on the matter distribution as well as cosmological constant. Finally, we compare the stable structure of wormhole for these equations of state through length parameter.

Stability of Einstein-power-Maxwell (2+1)-dimensional wormholes

This paper is devoted to the study of stable and unstable geometrical structures of charged thin-shell wormholes constructed from Einstein-power-Maxwell black holes by using Visser cut and paste approach. We use Israel thin-shell formalism to evaluate the stress-energy tensor components of matter distribution located at the wormhole throat. The stability of thin-shell is investigated by using equations of state (phantom-like and generalized Chaplygin gas model) for exotic matter and radial perturbation about equilibrium throat radius. We conclude that stable regions increase by increasing the charge parameter.

Influence of Linear Plus Quadratic Interactions Between Dark Components of the Universe on Thermodynamics

We work with the holographic model of interacting dark sector (dark energy plus dark matter) of the universe. The generalized Chaplygin gas model is taken as a Dark Energy (DE) candidate, and it interacts with Cold Dark Matter (CDM) in the framework of linear plus quadratic equation of state (EoS) parameter. We study the effect of interaction on the thermodynamics of the universe. Three interaction parameters of DE-CDM are considered: ΓρDE, ΓρDM, and Γ(ρDE + ρDM). We derive the corresponding effective equation of states for these different interaction parameters and analyze the behaviors of the derivative of entropies for DE, CDM and the apparent horizon, which is considered as a boundary of the universe. For this purpose the Generalized Second Law (GSL) of thermodynamics is used in the Friedman- Robertson-Walker (FRW) space to analyze the effect of quadratic terms on the thermodynamics of the universe, and the results are analyzed and compared with the solution for the linear form given in the literature.