Variable Modified Chaplygin Gas Research Articles

A Probe into the Evolution of Primordial Perturbations in the f(T) Gravity Framework with Chaplygin Gas

This work is focused on studying the cosmology of variable modified Chaplygin gas (VMCG) in the framework of exponential and logarithmic f(T) theory. The equation of state (EoS) for VMCG in exponential and logarithmic f(T) gravity shows quintom behavior. Primordial perturbations were studied for VMCG in both exponential and logarithmic f(T) gravity, and it was observed that the potential increases with cosmic time t, and the scalar field decreases toward the minimum value of the potential. The squared speed of sound was positive, meaning that VMCG in both exponential and logarithmic f(T) gravity shows stability against small gravitational perturbations.

Gravitational lensing of dark energy models and ΛCDM using observational data in loop quantum cosmology

This paper investigates the accelerated cosmic expansion in the late Universe by examining two dark energy models, viscous modified Chaplygin gas (VsMCG) and variable modified Chaplygin gas (VMCG), within loop quantum cosmology alongside the ΛCDM model. The objective is to constrain cosmic parameters using the ΛCDM model and 30 of the latest H(z) measurements from cosmic chronometers (CC), including Type Ia Supernovae, Gamma-Ray Bursts (GRB), Quasars, and 24 uncorrelated baryon acoustic oscillations (BAO) measurements across a redshift range from 0.106 to 2.33. The latest Hubble constant measurement from Riess in 2022 is included to enhance constraints. In the ΛCDM, VsMCG, and VMCG frameworks, best-fit parameters for the Hubble parameter (H0) and sound horizon (rd) are obtained. The results highlight significant disparities between H0 and rd values from late-time observational measurements, reflecting the known H0 and rd tensions. The gravitational lensing optical depth of the two dark energy models is studied by plotting log⁡(τ(zl)/H0−3τN) vs zl. The probability of finding gravitational lenses (optical depth) in both models increases with lens redshift zl. The change in optical depth behavior for different parameter constraints is graphically analyzed. A joint analysis of VsMCG and VMCG with ΛCDM is conducted. While the models diverge in the early Universe, they are indistinguishable at low redshift. Using the Akaike information criteria, the analysis indicates that neither dark energy model can be dismissed based on the latest observations.

Gravitational lensing: dark energy models in non-flat FRW Universe

In a non-flat FRW model, we have considered our Universe to be filled with non-interacting dark energy and dark matter. For the dark energy models, we have assumed Tachyonic Field (TF), Generalized Cosmic Chaplygin Gas (GCCG), New Variable Modified Chaplygin Gas (NVMCG), Modified Chaplygin–Jacobi Gas (MCJG), and Modified Chaplygin–Abel Gas (MCAG). We then analyzed these dark energy models with varying cosmological parameters in their optical depth behaviour and presented our result graphically. Later on, a comparison of our findings of the corresponding models in flat and non-flat Universe with the Lambda CDM model has also been presented.

Thermodynamic analysis for Non-linear system (Van-der-Waals EOS) with viscous cosmology

The following paper is motivated by the recent works of Kremer [Gen Relativ Gravit 36(6):1423–1432, 2004; Phys Rev D 68(12):123507, 2003], Vardiashvili (Inflationary constraints on the van Der Waals equation of state, arXiv:1701.00748, 2017), Jantsch (Int J Mod Phys D 25(03):1650031, 2016), Capozziello (Phys Lett A 299(5–6):494–498, 2002) on Van-Der-Waals EOS cosmology. The main aim of this paper is to analyze the thermodynamics of a Non-linear system which in this case is Van-Der-Waals fluid EOS (Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003). We have investigated the Van-Der-Waals fluid system with the generalized EOS as p=wleft( rho ,t right) rho +fleft( rho right) -3eta left( H,t right) H (Brevik et al., Int J Geom Methods Mod Phys 15(09):1850150, 2018). The third term signifies viscosity which has been considered as an external parameter that only modifies pressure but not the density of the liquid. The w(rho ,t) and f(rho )are the two functions of energy density and time that are different for the 3 types of Vander Waal models namely one parameter model, two parameters model and three parameters model (Ivanov and Prodanov, Eur Phys J C 79(2):118, 2019; Elizalde and Khurshudyan, Int J Mod Phys D 27(04):1850037, 2018). The value of EOS parameter (w_{EOS}) (Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003; Obukhov and Timoshkin, Russ Phys J 60(10):1705–1711, 2018) will showdifferent values for different models. We have studied the changes in the parameters for different cosmic phases [Kremer, Phys Rev D 68(12):123507, 2003; Capozziello et al., Phys Lett A 299(5–6):494–498, 2002; Capozziello et al., Quintessence without scalar fields, arXiv:astro-ph/0303041, 2003]. We have also studied the thermodynamics and the stability conditions for the three models in viscous condition [Obukhov and Timoshkin, Russ Phys J 60(10):1705–1711, 2018; Panigrahi and Chatterjee, Gen Relativ Gravit 49(3):35, 2017; Panigrahi and Chatterjee, J Cosmol Astropart Phys 2016(05):052, 2016; Chakraborty et al., Evolution of FRW Universe in Variable Modified Chaplygin Gas Model, arXiv:1906.12185, 2019]. We have discussed the importance of viscosity (Brevik and Grøn, Astrophys Space Sci 347(2):399–404, 2013) in explaining accelerating universe with negative pressure (Panigrahi and Chatterjee, Gen Relativ Gravit 49(3):35, 2017).Finally, we have resolved the finite time future singularity problems [Brevik et al., The effect of thermal radiation on singularities in the Dark Universe, arXiv:2103.08430, 2021; Odintsov and Oikonomou, Phys Rev D 98(2):024013, 2018; Odintsov and Oikonomou, Int J Mod Phys D 26(08):1750085, 2017; Frampton et al., Phys Rev D 85(8):083001, 2012; Frampton et al., Phys Lett B 708(1–2):204–211, 2012; Frampton et al., Phys Rev D 84(6):063003, 2011] and discussed the thermodynamics energy conditions [Visser and Barcelo, Energy conditions and their cosmological implications. In: Cosmo-99, pp 98–112, 2000; Chattopadhyay et al., Eur Phys J C 74(9):1–13, 2014; Arora et al., Phys. Dark Universe 31:100790, 2021; Sharma and Pradhan, Int J Geom Methods Mod Phys 15(01):1850014, 2018; Sahoo et al., AstronomischeNachrichten 342(1–2):89–95, 2021; Yadav et al., Mod Phys Lett A 34(19):1950145, 2019; Sharma et al., Int J Geom Methods Mod Phys 17(07):2050111, 2020, Moraes and Sahoo, Eur Phys J C 77(7):1–8, 2017; Hulke et al., New Astron 77:101357, 2020; Singla et al., Gravit Cosmol 26(2):144–152, 2020; Sharif et al., Eur Phys J Plus 128(10):1–11, 2013] with those models.

Thermal stability of Chaplygin gas models and Chevallier–Polarski–Linder parametrization

We consider the fractal universe model with timelike fractal profile in flat Friedmann–Robertson–Walker (FRW) universe model and check the thermodynamic stability of various dark energy models. These dark energy models include family of Chaplygin gas models (such as generalized Chaplygin gas, modified Chaplygin gas, generalized cosmic Chaplygin gas, variable modified Chaplygin gas) and parametrized equation-of-state (Chevallier–Polarski–Linder) model. To check the stability of these models in fractal framework thermodynamically, we construct total equation-of-state parameter for each case. The conditions to check the stability of models depending on some thermodynamic quantities yield three conditions on this parameter. We graphically check the behavior of the equation-of-state parameter along with stability of each model. It is concluded that the dark energy models are thermodynamically stable under appropriate choices of model parameters.

Gravitational waves for some dark energy models in FRW Universe

We study the gravitational waves phenomena for generalized Chaplygin gas, variable modified Chaplygin gas and some parametrizations of dark energy models. Motivated by their works, here we consider the Friedmann–Robertson–Walker (FRW) model of the non-flat Universe in the presence of dark matter with dark energy and we investigate the gravitational waves phenomena for some other candidates of dark energy like tachyonic field, generalized cosmic Chaplygin gas, new variable modified Chaplygin gas and Van der Waals fluid. By considering the individual conservation laws of dark matter and the dark energy components, we obtain the solutions of energy densities of the dark matter and dark energy components separately in terms of redshift. Next, we get the evolution equation for gravitational waves in FRW Universe. Then we analyze the natures of wave curves and their power spectrums for tachyonic field, generalized cosmic Chaplygin gas, new variable modified Chaplygin gas, and Van der Waals fluid.

Gravitational waves for variable modified Chaplygin gas and some parametrizations of dark energy in the background of FRW universe

In this work, we assume the Friedmann–Robertson–Walker (FRW) model of the non-flat Universe composed of dark matter and dark energy. Here the dark energy components are variable modified Chaplygin gas (VMCG) and some well-known parametrizations (models I–XIII). We assume that the dark matter and the dark energy are separately conserved. So the solutions of energy densities of the dark matter and dark energy are obtained in terms of observable quantities and the parameters associated with the models. Next we obtain the evolution equation for gravitational wave in the background of FRW Universe. Due to numerical analysis, we obtain the wave curve for VMCG and other dark energy models (models I–XIII). We investigate the power spectrum of the gravitational wave for VMCG and parametrizations of dark energy models I–XIII in diagrammatically.

Bouncing universe in the contexts of generalized cosmic Chaplygin gas and variable modified Chaplygin gas

In this work, we have considered the Friedmann-Robertson-Walker (FRW) model of the universe where bounce occurs and the universe is filled with Generalized Cosmic Chaplygin Gas (GCCG) or Variable Modified Chaplygin Gas (VMCG). We have studied the stability analysis through dynamical system for both models and found the critical points in flat, open and closed universe. In presence of scalar field, the dynamical behavior of scale factor and Hubble parameter is described in both models. Finally, we have analyzed the energy conditions for both the models in bouncing universe.

LRS Bianchi type-V universe with variable modified Chaplygin gas in a scalar–tensor theory of gravitation

The spatially homogeneous and anisotropic LRS Bianchi type-V Universe filled with variable modified Chaplygin gas in the framework of the Brans–Dicke (Brans and Dicke. Phys. Rev. 124, 925 (1961). doi:10.1103/PhysRev.124.925) scalar–tensor theory of gravitation has been studied. To obtain a determinate solution of the field equations we have used the condition that scalar field ([Formula: see text]) is a function of average scale factor. Some physical and kinematical properties of the model are discussed. We have also analyzed the stability of the solution.

Thermodynamics of the variable modified Chaplygin gas

A cosmological model with a new variant of Chaplygin gas obeying an equation of state(EoS), P = Aρ − B/ρα where B= B0an is investigated in the context of its thermodynamical behaviour. Here B0 and n are constants and a is the scale factor. We show that the equation of state of this `Variable Modified Chaplygin gas' (VMCG) can describe the current accelerated expansion of the universe. Following standard thermodynamical criteria we mainly discuss the classical thermodynamical stability of the model and find that the new parameter, n introduced in VMCG plays a crucial role in determining the stability considerations and should always be negative. We further observe that although the earlier model of Lu explains many of the current observational findings of different probes it fails the desirable tests of thermodynamical stability. We also note that for 0n < our model points to a phantom type of expansion which, however, is found to be compatible with current SNe Ia observations and CMB anisotropy measurements. Further the third law of thermodynamics is obeyed in our case. Our model is very general in the sense that many of earlier works in this field may be obtained as a special case of our solution. An interesting point to note is that the model also apparently suggests a smooth transition from the big bang to the big rip in its whole evaluation process.

Cosmological constraints on the variable modified Chaplygin gas model by using MCMC approach

We investigate the cosmological constraints on the variable modified Chaplygin gas (VMCG) model from the latest observational data: Union2 dataset of Type Ia supernovae (SNIa), the observational Hubble data (OHD), the baryon acoustic oscillations (BAO) and the cosmic microwave background (CMB) data. By using the Markov chain Monte Carlo (MCMC) method, we obtain the mean values of parameters in the flat model: [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. Furthermore, we investigate the thermodynamical properties of VMCG model at apparent horizon, event horizon and particle horizon respectively.

Observational Data Fitting to Constrain Variable Modified Chaplygin Gas in the Background of Horava-Lifshitz Gravity

FRW universe in Horava-Lifshitz (HL) gravity model filled with a combination of dark matter and dark energy in the form of variable modified Chaplygin gas (VMCG) is considered. The permitted values of the VMCG parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters Ω d m0, Ω v m c g0, H 0, redshift z and other parameters like α, A, γ and n. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the χ 2 test. The best-fit values of the parameters are obtained by 66 %, 90 % and 99 % confidence levels. Next due to joint analysis with BAO and CMB observations, we have also obtained the bounds of the parameters (A, γ) by fixing some other parameters α and n. The best fit value of distance modulus μ(z) is obtained for the VMCG model in HL gravity, and it is concluded that our model is perfectly consistent with the union2 sample data.

Higher order corrections of the extended Chaplygin gas cosmology with varying $$G$$ G and $$\Lambda $$ Λ

In this paper, we study two different models of dark energy based on Chaplygin gas equation of state. The first model is the variable modified Chaplygin gas while the second one is the extended Chaplygin gas. Both models are considered in the framework of higher order $f(R)$ modified gravity. We also consider the case of time varying gravitational constant $G$ and $\Lambda$ for both models. We investigate some cosmological parameters such as the Hubble, the deceleration and the equation of state parameters. Then we showed that the model that we considered, extended Chaplygin gas with time-dependent $G$ and $\Lambda$, is consistent with the observational data. Finally we conclude with the discussion of cosmological perturbations of our model.

Accretions of various types of dark energies onto Morris–Thorne wormhole

In this work, we have studied the accretion of dark energies onto a Morris–Thorne wormhole. Previously, in ref. (González-Díaz, arXiv:hep-th/0607137 ), it was shown that for quintessence like dark energy, the mass of the wormhole decreases, and for phantom like dark energy, the mass of the wormhole increases. We have assumed two types of dark energy: the variable modified Chaplygin gas and the generalized cosmic Chaplygin gas. We have found the expression of the wormhole mass in both cases. We have found the mass of the wormhole at late universe and this is finite. For our choices of the parameters and the function $$B(a)$$ , these models generate only quintessence dark energy (not phantom) and so the wormhole mass decreases during the evolution of the universe. Next we have assumed the five kinds of parametrizations of well-known dark-energy models. These models generate both quintessence and phantom scenarios i.e., phantom crossing models. So if these dark energies accrete onto the wormhole, then for the quintessence stage, the wormhole mass decreases up to a certain value (a finite value) and then again increases to an infinite value for the phantom stage during whole evolution of the universe. That means that if the five kinds of DE accrete onto a wormhole, the mass of the wormhole decreases up to a certain finite value and then increases in the late stage of the evolution of the universe. We have also shown these results graphically.

Gravitational Collapse with Dark Energy and Dark Matter in Hořava-Lifshitz Gravity

In this work, the collapsing process of a spherically symmetric star, made of dust cloud, is studied in Hořava Lifshitz gravity in the background of Chaplygin gas dark energy. Two different classes of Chaplygin gas, namely, New variable modified Chaplygin gas and generalized cosmic Chaplygin gas are considered for the collapse study. Graphs are drawn to characterize the nature and to determine the possible outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different dark energy models. It is found that for open and closed universe, collapse proceeds with an increase in black hole mass, the only constraint being that, relatively smaller values of Λ has to be considered in comparison to λ. But in case of flat universe, possibility of the star undergoing a collapse in highly unlikely. Moreover it is seen that the most favourable environment for collapse is achieved when a combination of dark energy and dark matter is considered, both in the presence and absence of interaction. Finally, it is to be seen that, contrary to our expectations, the presence of dark energy does not really hinder the collapsing process in case of Hořava-Lifshitz gravity.

Universe Described by Variable Modified Chaplygin Gas with Statefinder Diagnostic in General Relativity

The universe filled with variable modified Chaplygin gas having the equation of state p=Aρ−B/ρ α , where 0≤α≤1, A is a positive constant and B is a positive function of the average scale factor a(t) of the universe (i.e. B=B(a)) is studied within the framework of general relativity. The new class of exact solutions of Einstein’s field equations is derived by using a time dependent deceleration parameter. The cosmic jerk parameter in our derived model is in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed statefinder parameters, the behavior of different stages of the universe is studied. The physical and kinematical properties of cosmological models are also discussed.

Constraining the Parameters of New Variable Modified Chaplygin Gas Model

Assuming the flat FRW universe in Einstein’s gravity filled with New Variable Modified Chaplygin gas (NVMCG) dark energy and dark matter having negligible pressure. In this research work we analyze the viability on the basis of recent observation. Hubble parameter H is expressed in terms of the observable parameters H 0, $\varOmega_{m}^{0}$ and the model parameters A 0, B 0, C 0, m, n, α and the red shift parameter z. Here we find a best fitted parameter range of A 0, B 0 keeping 0≤α≤1 and using Stern data set (12 points) by minimizing the χ 2 test at 66 %, 90 % and 99 % confidence levels. Next we do the joint analysis with BAO and CMB observations. Again evaluating the distance modulus μ(z) vs redshift (z) curve obtained in the model NVMCG with dark matter with the best fitted value of the parameters and comparing with that derived from the Union2 compilation data.

Correspondence of F-essence with Chaplygin gas cosmology

In this work, we have considered generalized cosmic Chaplygin gas (GCCG) and new variable modified Chaplygin gas (NVMCG) types of dark energies in the framework of F -essence cosmology and investigated the consequences for their co-existence. The correspondence of the F -essence with the above types of Chaplygin gas models has been investigated. The natures of K and Y for this correspondence of the F -essence with all the gases have been analyzed graphically. From the graphical representation, we demand that K always increases with Y due to correspondence, and the EoS parameter w shows that the F -essence model always gives only quintessence type of dark energy and phantom crossing does not happen in our constructed models.

How effective is new variable modified Chaplygin gas to play the role of dark energy—a dynamical system analysis in RS II brane model

Motivated by some previous works of Rudra et al. we set to explore the background dynamics when dark energy in the form of New Variable Modified Chaplygin gas is coupled to dark matter with a suitable interaction in the universe described by brane cosmology. The main idea is to find out the efficiency of New variable modified Chaplygin gas to play the role of DE. As a result we resort to the technique of comparison with standard dark energy models. Here the RSII brane model have been considered as the gravity theory. An interacting model is considered in order to search for a possible solution of the cosmic coincidence problem. A dynamical system analysis is performed because of the high complexity of the system. 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 and get an insight into the effectiveness of the dark energy model. It is also seen that the background dynamics of New Variable Modified Chaplygin gas is consistent with the late cosmic acceleration. After performing an extensive mathematical analysis, we are able to constrain the parameters of new variable modified Chaplygin gas as m<n to produce the best possible results. Future singularities are studied and it is found that the model has a tendency to result in such singularities unlike the case of generalized cosmic Chaplygin gas. Our investigation leads us to the fact that New Variable Modified Chaplygin gas is not as effective as other Chaplygin gas models to play the role of dark energy.

Variable Modified Chaplygin Gas in Anisotropic Universe with Kaluza-Klein Metric

In this work, we have considered Kaluza-Klein Cosmology for anisotropic universe where the universe is filled with Variable Modified Chaplygin Gas (VMCG). Here we find normal scalar field ϕ and the self interacting potential V(ϕ) to describe the VMCG Cosmology. We have also graphically analyzed the geometrical parameters named Statefinder Parameters in anisotropic Kaluza-Klein model. Next, we have considered a Kaluza-Klein model of interacting VMCG with dark matter in the Einstein gravity framework. Here we construct the three dimensional autonomous dynamical system of equations for this interacting model with the assumption that the dark energy and the dark matter interacts between themselves and for that we also choose the interaction term. We convert that interaction term to its dimensionless form and perform stability analysis and solve them numerically. We obtain a stable scaling solution of the equations in Kaluza-Klein model and graphically represent solutions.