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.

Cosmology in f (R, T) modified gravity : unified dark matter and dark energy model constrained by current observations

The proposed cosmological model deals with modified Chaplygin gas (MCG) in f(R, T) = R + ξ(T) gravity, where R is the Ricci Scalar and T is the trace of energy-momentum tensor. The function ξ(T) is chosen as the linear combination of power law and logarithmic form under flat Friedmann-Lemaitre-Robertson-Walker space-time. The model is compatible with current observational data (Pantheon Type Ia Supernova) and confronts the deceleration and state parameters effectively. The model can predict the Big Rip in future infinity and can also tackle the difficulties related to the fine-tuning and the coincidence problem practically. Further, we have numerically solved the modified Friedmann equations in f(R, T) gravity and also performed a Markov Chain Monte Carlo analysis to obtain the best fit parameters of this current cosmological model. These best parameters are then used to compute the cosmographic parameters, i.e., the deceleration parameter, the jerk parameter and the snap parameter. Significantly, the cosmographic test has given valuable insights into the dynamics of the current cosmological model and also enriched us to understand about the cosmic evolution of the accelerated Universe. Additionally, the Statefinder diagnostics and O m diagnostics have provided deeper insights into the dynamics of the cosmic expansion and also provided information to distinguish between both the cosmological frameworks. Furthermore, these tests also reveal that at late times, the current model goes beyond the phantom region. Again, the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) have provided enough support for the current model under consideration, indicating that the present model exhibits a plausible explanation. However, the ΛCDM model has emerged with the lowest AIC value which suggests its relatively superior fit compared to the current model. Finally, our current model aligns well with several recent observations and unveils various intriguing features about the late time accelerated Universe.

Simple waves for anti-van der Waals modified Chaplygin gas in 2-D magnetohydrodynamics

Abstract This paper presents essential findings on the reducible equations introduced by Courant and Friedrichs in their seminal work, Supersonic Flow and Shock Waves. In this paper, we discuss the presence of simple waves in a 2-D magnetohydrodynamic system with an anti-van der Waals-modified Chaplygin gas. Following the approach of Hu and Sheng (characteristic decomposition of the 2 × 2 quasilinear strictly hyperbolic systems). Appl. Math. Lett. 25(3), 262–267 (2012), and (simple waves and characteristic decompositions of quasilinear hyperbolic systems in two independent variables). Math. Methods Appl. Sci. 38(8), 1494–1505 (2015) for the characteristic decomposition of a strictly hyperbolic system, we establish the existence of simple waves for a non-reducible system. This extends Courant and Friedrichs’s fundamental finding, which was initially proposed for reducible system (R. Courant and K. O. Friedrichs, Supersonic Flow and Shock Waves, New York, Interscience Publishers, Inc, 1948, p. 464). These results enhance our understanding of simple wave behaviour in magnetohydrodynamic systems with modified Chaplygin gas, expanding the applicability of Courant and Friedrichs’s theoretical framework.

Constraining the parameters of generalized and viscous modified Chaplygin gas and black hole accretion in Einstein-Aether gravity

In this paper, we investigate the phenomenon of the accelerated cosmic expansion in the late universe and the mass accretion process for a four-dimensional Einstein-Aether black hole. Starting with the basics of Einstein-Aether gravity theory, we first consider the field equations and two well-known models of Chaplygin gas, i.e., the generalized cosmic Chaplygin gas model and viscous modified Chaplygin gas model. We then obtain the energy density and Hubble parameter equations for these models in terms of various dimensionless density parameters and some unknown parameters. After finding the required parameters, we proceed with the mass accretion process. For both models, we obtain the equation of mass in terms of the redshift function and graphically represent the change in the mass of the black hole with a redshift. At the same time, we perform a graphical comparison between these models and the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Lambda $$\\end{document}CDM model of the universe. Finally, we conclude that the mass of a four-dimensional black hole will increase along the evolution of the universe within the framework of Einstein-Aether gravity.

Viscous modified Chaplygin gas with spherical top-hat collapse in modified theories of gravity

Abstract The work explores the dynamics of a spherically symmetric perturbation of viscous modified Chaplygin
gas (VMCG) in different gravity theories within the spherical top hat collapse framework (SC-TH). The
study investigates the behaviour of perturbed quantities such as the δ, θ, w, wc, c2
s , c2
e , and h using numer-
ical and graphical analysis. Our findings reveal that VMCG generates quintessential dark energy without
crossing over to the phantom barrier in most of the gravity models considered here. Further, in all the
gravity models considered here, VMCG remained classically stable. This research offers new insights into
the evolution of VMCG in different gravitational contexts. In this paper, we have examined the collapse of
viscous modified Chaplygin gas in the context of (i) Einstein’s gravity, (ii) Loop quantum cosmology, (iii)
generalised Rastall gravity, and (iv) the fractal universe. We have also addressed their comparative analysis.

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.

Isolated compact star RXJ1856.5 − 3754 in f(R,T) modified gravity in Tolman-Kuchowicz spacetime

Our main motive is to model and study the mass-radius relation of the specific isolated compact star RXJ1856.5−3754 in the background of the late time accelerated Universe and to achieve the equation of state of the core matter under stable equilibrium in f(R,T) modified gravity using Tolman-Kuchowicz metric potentials. Einstein-Hilbert action is taken as f(R,T)=R+2ξT, where R and T are the Ricci scalar and the trace of energy-momentum tensor respectively and ξ as coupling parameter. Modified Tolman-Oppenheimer-Volkoff equations are numerically solved by considering the presence of modified Chaplygin gas inside the star and also solving the corresponding field equations. We have got an explicit scenario of the structural evolution of isolated neutron stars through accelerating spacetime. Interestingly, all the derived outcomes of this investigation have become compatible with physically adopted regimes which reveal the physical viability of this current model.

Observational analysis on warm tachyon scalar field inflation via Woods–Saxon, valley hybrid, exponential, quartic, quasi exponential potentials

In this paper, we study the tachyon scalar field inflationary scenario considering FRW universe in context of modified Chaplygin gas model. For this purpose, we consider some well-known potential models such as Woods–Saxon potential , Valley hybrid potential, exponential potential, quartic potential, and Quasi exponential potential. We develop the relations for the number of e-folds N, slow roll parameters ϵ,η, scalar spectral index ns, scalar to tensor ratio r, and running scalar spectral index αs. To understand how the inflationary parameters behave, the planes of ns−r and ns−αs are plotted. Through these plotted planes, we check the consistency of these inflationary parameters for assumed potentials in light of the Planck 2018 observational data and compare our outcomes with these observation by incorporating observational contours. We found that the obtained results are compatible and consistent with the recent observational data.

Reconstruction schemes of scalar field models for the Power Law Entropy Corrected Holographic Dark Energy model with Ricci scalar cut-off

In this work, we examine the cosmological characteristics of the Power Law Entropy Corrected Holographic Dark Energy (PLECHDE) model with infrared (IR) cut-off, which is determined by the curvature parameter k, the time derivative of H, and the average radius of the Ricci scalar curvature R, which varies with the Hubble parameter H squared. We obtain the deceleration parameter q and the Equation of State (EoS) parameter of Dark Energy (DE) ωD. Additionally, we derive the Hubble parameter H and the scale factor a expressions as functions of the cosmic time t. Additionally, we examine the limiting scenario that pertains to a flat Dark Dominated Universe. Furthermore, we establish a correspondence between the DE model considered and some scalar fields, in particular the Generalized Chaplygin Gas, the Modified Chaplygin Gas, the Modified Variable Chaplygin Gas, the New Modified Chaplygin Gas, the Viscous Generalized Chaplygin Gas, the Dirac–Born–Infeld, the Yang–Mills, and the Non Linear Electrodynamics scalar field models.

Critical behavior and Joule-Thomson expansion of charged AdS black holes surrounded by exotic fluid with modified Chaplygin equation of state* *Supported by the Doctoral Foundation of Zunyi Normal University of China (BS [2022]07, QJJ-[2022]-314), and the National Natural Science Foundation of China (12265007, 12264061). The research partially was supported by the Long-Term Conceptual Development of a University of Hradec Králové

By considering the concept of a unified single fluid model, referred to as modified Chaplygin gas (MCG), which amalgamates dark energy and dark matter, we explore the thermodynamic characteristics of charged anti-de Sitter (AdS) black holes existing in an unconventional fluid accompanied by MCG. To accomplish this objective, we derive the equations of state by regarding the charge as a thermodynamic variable. The effects of MCG parameters on the critical thermodynamic quantities ( , , ) are examined, followed by a detailed analysis of the diagram. To provide a clearer explanation of the phase transition, we present an analysis of the Gibbs free energy. It is important to note that if the Hawking temperature exceeds the critical temperature, a distinct pattern is observed known as swallowtail behavior. This indicates that the system undergoes a first-order phase transition from a smaller black hole to a larger one. The critical exponent of the system is found to be in complete agreement with that of the van der Waals fluid system. Furthermore, we investigate the impact of MCG parameters and black hole charge on Joule-Thomson (J-T) expansion in the extended phase space. The J-T coefficient is examined to pinpoint the exact region experiencing cooling or heating, and the observation reveals that the presence of negative heat capacity results in the occurrence of a cooling process. The impact of MCG on the inversion curve of charged black holes exhibits a striking resemblance to that observed in most multi-dimensional black hole systems. In addition, it is worth noting that certain parameters exert a significant influence on the ratio . For specific values of the MCG parameters, the ratio is consistent with the charged AdS black hole. The parameters γ and β have a non-negligible effect on the isenthalpic curve.

Phase structure of charged AdS black holes surrounded by exotic fluid with modified Chaplygin equation of state

By considering the concept of the modified Chaplygin gas (MCG) as a single fluid model unifying dark energy and dark matter, we construct a static, spherically charged black hole (BH) solution in the framework of General Relativity. The P–V criticality of the charged anti-de Sitter (AdS) BH with a surrounding MCG is explored in the context of the extended phase space, where the negative cosmological constant operates as a thermodynamical pressure. This critical behavior shows that the small/large BH phase transition is analogous to the van der Waals liquid/gas phase transition. Accordingly, along the P–V phase spaces, we derive the BH equations of state and then numerically evaluate the corresponding critical quantities. Similarly, critical exponents are identified, along with outcomes demonstrating the scaling behavior of thermodynamic quantities near criticality to a universal class. The use of geometrothermodynamic (GT) tools finally offers a new perspective on the discovery of the critical phase transition point. At this stage, we apply a class of GT tools, such as Weinhold, Ruppeiner, HPEM, and Quevedo classes I and II. The findings are therefore non-trivial, as each GT class metric captures at least either the physical limitation point or the phase transition critical point. Overall, this paper provides a detailed study of the critical behavior of the charged AdS BH with surrounding MCG.

Role of modified Chaplygin gas in Little Rip phenomena from interaction between dark energy and dark matter

In this article, an interacting dark energy (DE)- dark matter (DM) scenario has been considered in a flat Friedmann–Lemaitre–Robertson–Walker (FLRW) cosmological model, where DE has a variable equation-of-state that follows the modified Chaplygin-like equation of state (Eq. (1)) characterized by two time dependent parameters Λ(t) and ω(t) and DM has a non-zero equation of state pDM=ω̃ρDM. Gravitational equations of motion for dark matter have been solved for two different cases of thermodynamic parameter ω̃ as ω̃=constant and ω̃≠ constant. Also, it has been found that Λ(t)→−∞ as t→∞, it shows that the fate of our universe depends on specific model parameters for the coupled dark energy and dark matter, and experiences Little Rip behavior. Also, it is observed that coupled dark energy and dark matter may inflate and expand the universe after the Big Bang in the far future.

The limiting behavior of Riemann solutions to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force

In this paper, we investigate the limiting behavior of Riemann solutions to the Euler equations of compressible fluid flow for modified Chaplygin gas with the body force as the two parameters tend to zero. The formation of delta shock waves and the vacuum states is identified and analyzed during the process of vanishing pressure in the Riemann solutions. The concentration and cavitation are fundamental and physical phenomena in fluid dynamics, which can be mathematically described by delta shock waves and vacuums, respectively. In this paper, our main objective is to rigorously investigate the formation of delta shock waves and vacuums and observe the concentration and cavitation phenomena. First, the Riemann problem of the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force is solved. Second, we rigorously confirm that, as the pressure vanishes, any two shock Riemann solution to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force tends to a δ-shock solution to the pressureless gas dynamics model with a body force, and the intermediate density between the two shocks tends to a weighted δ-measure that forms the δ-shock; any two-rarefaction-wave Riemann solution to the Euler equations of compressible fluid flow for the modified Chaplygin gas with the body force tends to a solution consisting of four contact discontinuities together with vacuum states with three different virtual velocities in the limiting situation.

Nuclear matter equation of state and stability of charged compact stars embedded in f(T) modified gravity, under cosmic acceleration

This work mainly focuses on modeling the charged compact stars and investigating their properties in the framework of [Formula: see text] modified gravity, under the accelerated phase of the universe. In this study, we have introduced the modified gravity and dark matter to culture the evolution of the charged neutron stars by considering the present situation. True knowledge and proper study on the macroscopic parameters of the compact stars are very much needed to realize the microscopic properties and behavior of the core nuclear matter at very high density and pressure. The existence of modified Chaplygin gas as an exotic fluid inside the core of these stars in [Formula: see text] gravity plays a very important role inside the stars. We have found out that exotic fluid has a great impact on the equation of state of the core nuclear matter and even on the stability of the compact stars. Pressure anisotropy reduces the tidal deformability of the charged stars in an appreciable amount and helps to get a more compact structure. But surprisingly, the compact stars are still able to maintain their spherically stable and equilibrium configuration. Further, we can put constraints on several macroscopic parameters of the compact stars and can investigate their evolution from our present investigation.

Thin-shell wormholes and modified Chaplygin gas with relativistic corrections

In this paper, we analyze thin-shell wormholes from two identical copies of charged static cylindrically symmetric spacetimes using Visser’s ‘cut and paste’ approach under the influence of f(R, T) gravity Harko, Lobo, Nojiri, and Odintsov (2011, Phys. Rev. D 84, 024020). In this scenario, the modified Chaplygin gas supports the exotic matter in the shell which allows, one to examine the dynamics of constructed wormholes. We utilize the junction condition to connect the interior and exterior geometries across the hypersurface and calculate different components of the Lanczos equation recently computed by Roza in Rosa (2021, Phy. Rev. D 103, 104069). We analyze the stability of the thin-shell wormhole models under linear perturbations while keeping the cylindrical symmetry and also examine the influence of charge on their stability. The positive quantity of the second derivative of potential at the throat radius might be interpreted as the stability criterion. We find both unstable and stable wormhole solutions for different parameters included in the equation of state and specific forms of considered gravity and illustrate them theoretically as well as graphically. We examine the impact of electric charge on the stability region of a constructed wormhole, which suggests that a wormhole model with a charge may exhibit more stable behavior compared to an uncharged system.

Anisotropic Universes Sourced by Modified Chaplygin Gas

In this work, we perform a comparative study of the Kantowski–Sachs (KS) and Bianchi-I anisotropic universes with Modified Chaplygin gas (MCG) as matter source. We obtain the volume and scale factors as solutions to the Einstein Field Equations (EFEs) for the anisotropic universes, and check whether the initial anisotropy is washed out or not for different values of the MCG parameters present in the solution by obtaining the anisotropy parameters for each solution. The deceleration parameter is also obtained for each solution, the significance of which is discussed in the concluding section. Interestingly there are a number of notable results that appear from our study which help us to compare and contrast the two different anisotropic models along with proper understanding of the role of MCG as matter source in these models.

Observational constraints in modified Chaplygin gas cosmological model

Bianchi type-V cosmological model with modified Chaplygin gas having the equation of state p=γρ−Cρα, where C is a positive constant and 0≤α,γ≤1, has been investigated. To find the deterministic solution, we have considered power-law and intermediate expansions which predicts the decelerating and accelerating phases of expansion of the Universe. Here, we have also constructed cosmographic parameters like H,j,l,s∗ and studied their evolution in the background of Bianchi type-V Universe with modified Chaplygin gas. The geometric diagnostics, the state-finder (r,s) in our cosmological model to discriminate from the ΛCDM model are studied. We have performed the statistical analysis and obtained best fit values of the parameters using MCMC technique for intermediate model. We have also compared our models with observed Hubble data for both scenarios. We have noted some new and interesting cosmological solutions which is relevant for the model building, including present accelerating phase of the Universe.

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.

Dark Energy Star: Physical Constraints on the Bounds

AbstractIn the present article, we explore a new solution to the Einstein‐Maxwell field equations to describe spherically symmetric, charged and anisotropic dark energy stars. The interior of such stars containing two non‐interacting fluids like dark and normal matter with a relation that the dark energy density is proportional to the energy density of a isotropic matter. We have used modified chaplygin gas equation to define the dark energy part. Also we have defined the interior space‐time through Krori‐Barua (KB) space‐time and matched it with the exterior Reissner‐Nordström space‐time. The well‐behaveness of the physical attributes have been discussed by plotting graphs for three specific compact objects with respect to our solutions. We conclude that all the physical attributes satisfy the required conditions for viability as well as stability and hence our model can be used to characterize dark energy stars for a set of parametric values belong to the present study.

Effect of viscous generalized and modified Chaplygin gas on $$f (R, {\mathcal {G}}, {\mathcal {T}})$$ gravity

Effect of viscous generalized and modified Chaplygin gas on $$f (R, {\mathcal {G}}, {\mathcal {T}})$$ gravity