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In this paper, the structure of the generalized Vaidya space–time when the type-II of the matter field satisfies the equation of the state P = ρ is investigated. Satisfying all energy conditions, we show that this space–time contains the "eternal" naked singularity. It means that once the singularity is formed it will never be covered with the apparent horizon. However. in the case of the apparent horizon formation the resulting object is a white hole. We also prove that this space–time contains only null naked singularity. [ABSTRACT FROM AUTHOR]

In this paper, we study the 2-flavor equation of state of the quantum chromodynamics at zero temperature and finite chemical potentials with a modified Nambu–Jona–Lasinio model, where the beta equilibrium and electric charge neutrality conditions of the system (including u, d quarks, electrons and muons) are considered. The related chiral phase transition is also discussed in this paper. For comparison, we show the results with four different parameter sets, and find only quantitative differences. As chemical potential increases, the crossover instead of first-order chiral phase transition happens. Finally, we calculate the binding energy per baryon for different parameter sets, and find that the 2-flavor quark system with a smaller G1 (or a larger m) possesses the lower binding energy per baryon, indicated to be more stable than the other case. [ABSTRACT FROM AUTHOR]

In Einstein's General Relativity (GR), the gravitational interactions are described by the spacetime curvature. Recently, other alternative geometric formulations and representations of GR have emerged in which the gravitational interactions are described by the so-called torsion or non-metricity. Here, we consider the recently proposed modified symmetric teleparallel theory of gravity or f (Q) gravity, where Q represents the non-metricity scalar. In this paper, motivated by several papers in the literature, we assume the power-law form of the function f (Q) as f (Q) = α Q n + 1 + β , (where α , β , and n are free model parameters) that contains two models: Linear (n = 0) and nonlinear (n ≠ 0). Further, to add constraints to the field equations we assume the deceleration parameter form as a divergence-free parametrization. Then, we discuss the behavior of various cosmographic and cosmological parameters such as the jerk, snap, lerk, O m diagnostic, cosmic energy density, isotropic pressure, and equation of state (EoS) parameter with a check of the violation of the strong energy condition (SEC) to obtain the acceleration phase of the Universe. Hence, we conclude that our cosmological f (Q) models behave like quintessence dark energy (DE). [ABSTRACT FROM AUTHOR]

Achieving the potential for plasma particle interactions by modifying the Deutsch potential has been considered in many studies. One very convenient way to do this is to utilize the method as a dielectric function. In this method, by applying different potentials, it tries to provide corrective terms in the initial potential. As a result of using this method, an effective potential function is obtained from which the plasma characteristics including state equation and thermodynamic features can be derived. Because the screening effects between plasma particles are not taken into account by the Deutsch potential and therefore show different results from the real values, in this paper, we have tried to add corrective terms with the help of Hulthen potential and dielectric response function to it. Thus, an effective potential was obtained and then its equation of state was derived consequently. Finally, the results of this modified potential and the equation of state were compared with the results of other works. [ABSTRACT FROM AUTHOR]

In this paper, a multistage reciprocating compressor system is considered to study, analyze and improve its reliability by incorporating the redundancies using Markov approach. In Markov method, the reliability is assessed by creating state space model and deriving probabilistic equations of all the states. The developed equations are further solved with the help of a MATLAB. Constant failure and repair rates are considered for the different components in the system. Standby redundancy has been employed to enhance the system reliability. System reliability value for the basic system model, i.e. Model 1 at 10,000 h is 0.1252 that has been increased by using standby redundancies in Model 4 with no repair to 0.6428 and with repair to 0.9374. This work will be helpful to the manufacturers, users, researchers and others by the application, and implementation of the proposed methodology. [ABSTRACT FROM AUTHOR]

There are many ways to probe alternative theories of gravity, namely, via experimental tests at solar system scale, cosmological data and models, gravitational waves and compact objects. In this paper, we consider a model of gravity with torsion f (T) applied to compact objects such as neutron stars (NSs) for a couple of realistic equations of state (EOS). To do so, we follow our previous articles, in which we show how to model compact stars in f (T) gravity by obtaining its corresponding Tolman–Oppenheimer–Volkof equations. In this modeling of NS in f (T) gravity presented here, we calculate, among other things, the maximum mass allowed for a given realistic EOS, which would also allow us to evaluate which models are in accordance with the observations. The results already known to General Relativity must be reproduced to some extent and, eventually, we can find models that allow higher maximum masses for NSs than Relativity itself, which could explain, for example, the secondary component of the event GW190814, if this star is a massive NS. [ABSTRACT FROM AUTHOR]

In quantum gravity phenomenology, the effect of the generalized uncertainty principle (GUP) on white dwarf structure has been given much attention in recent literature. However, these studies assume a zero temperature equation of state (EoS), excluding young white dwarfs whose initial temperatures are substantially high. To that cause, this paper calculates the Chandrasekhar EoS and resulting mass-radius relations of finite temperature white dwarfs modified by the quadratic GUP, an approach that extends Heisenberg's uncertainty principle by a quadratic term in momenta. The EoS was first approximated by treating the quadratic GUP parameter as perturbative, causing the EoS to exhibit expected thermal deviations at low pressures, and conflicting behaviors at high pressures, depending on the order of approximation. We then proceeded with a full numerical simulation of the modified EoS, and showed that in general, finite temperatures cause the EoS at low pressures to soften, while the quadratic GUP stiffens the EoS at high pressures. This modified EoS was then applied to the Tolman–Oppenheimer–Volkoff equations and its classical approximation to obtain the modified mass-radius relations for general relativistic and Newtonian white dwarfs. The relations for both cases were found to exhibit the expected thermal deviations at small masses, where low-mass white dwarfs are shifted to the high-mass regime at large radii, while high-mass white dwarfs acquire larger masses, beyond the Chandrasekhar limit. Additionally, we find that for sufficiently large values of the GUP parameter and temperature, we obtain mass-radius relations that are completely removed from the ideal case, as high-mass deviations due to GUP and low-mass deviations due to temperature are no longer mutually exclusive. [ABSTRACT FROM AUTHOR]

In this paper, a complete lattice study of thorium telluride (ThTe) in the effects of three-body interaction (TBI) in the framework of RIM and RSM models is reported. By use of the present model, I have theoretically reported elastic constants, pressure derivatives, dispersion relation curve, specific heat curve, combined density of states (CDS) and equation of state of the ThTe compound. The achieved results are good with experimentally reported results and have given very important information about this compound for further investigation. [ABSTRACT FROM AUTHOR]

This paper further studies the cosmological evolution and geometry diagnosis of Barrow holographic dark energy (BHDE) in the DGP braneworld, specifically, by choosing the interaction between dark energy and dark matter item. Q 1 = 3 H ξ ρ de , Q 2 = 3 H ξ ρ dm , Q 3 = 3 H ξ ρ de 2 / (ρ de + ρ dm ) , Q 4 = 3 H ξ ρ dm 2 / (ρ de + ρ dm ) are discussed in the case of no interaction and four different interactions, the evolution laws of energy density parameters, deceleration parameters and EOS (equation of state) parameters of Barrow holographic dark energy. The results show that the Barrow holographic dark energy in the DGP braneworld conforms to the current cosmic evolution rule, already achieved the universe main ingredients from matter to the transition of energy, and explains the problem of cosmic acceleration. Further, in order to distinguish between the model and Λ CDM model, this paper also geometrically diagnoses the model with the two ways of Statefinder hierarchy and Om (z). From their respective evolution image you can see, these two kinds of diagnosis methods can not only distinguish different from Λ CDM model, but also can intuitively reflect the coupling parameters that can significantly affect the dark energy model. [ABSTRACT FROM AUTHOR]

This paper explores the existence of static wormholes in 4-Dimensional Einstein Gauss–Bonnet (4D EGB) gravity. We discuss some possibilities for constructing radial-dependent shape functions via different strategies to develop some non-conventional wormhole geometries by considering anisotropic matter sources. In this regard, we assume a specific form of the equation of state and investigate its effects on Gauss–Bonnet (GB) coupling parameter. Next, we impose a traceless condition on the anisotropic fluid distribution as well as radial-dependent energy density profile to explore wormhole geometries as separate cases. It is seen that the obtained results can be reduced into Morris–Throne wormholes for the zero value of GB-coupled parameter for anisotropic fluid distribution. Furthermore, we scrutinize flaring-out conditions and examine asymptotically flatness constraints for the existence of wormholes. Our analysis shows that the weak energy condition (WEC) is satisfied for a particular range by constraining GB-coupled parameter. We study the dynamics of GB-coupled parameter for both cases μ > 0 and μ < 0. It is concluded that wormhole solutions are possible for μ > 0 and, in some cases, μ < 0. The active gravitational mass of developed wormholes is calculated and plotted graphically. The wormhole geometry is discussed by plotting 2D and 3D embedding diagrams. In order to analyze the complexity of the system, we have plotted the complexity factor for each wormhole. [ABSTRACT FROM AUTHOR]

In this paper, we study a homogeneous and isotropic flat Friedmann–Robertson–Walker (FRW) universe in Rastall gravity, in which there exist the components of radiation and dust. That is to say, the density of fluid ρ γ satisfies the barotropic equation of state p γ = (γ − 1) ρ γ , where γ = 4 / 3 and 1 , and the equation of state w = γ − 1. We derive the modified Friedmann equations, and the effective equation of state w ̃ in this universe model. For the dust-dominated case, the effective equation of state w ̃ is described by λ − 1 3 λ − 1 , where λ is the Rastall parameter. As 1 3 < λ < 2 3 , we have w ̃ < − 1 3 which means an accelerated expansion of the universe occurs. Along with the conditions for the convergent modified Friedmann equations and the positive density of dust, the Rastall parameter λ should be in the range of (1 2 , 2 3). In other words, the various w ̃ for 1 2 < λ < 2 3 correspond to those of quintessence with the general barotropic equation of state (γ = 1). For the general case, the Rastall universe full of radiation and dust, the expression of w ̃ is complicated involving the Rastall parameter, the density of radiation and the density of dust. As the ratio of the densities of dust and radiation is smaller than 2 − 3 λ 2 (2 λ − 1) , w ̃ is less than − 1 3 . Moreover, to keep the density of dust positive, the Rastall parameter should be restricted in (1 2 , 2 3) too. By the numerical calculation, we find that w ̃ from 1 3 decreases as N (N ≡ l n a (t)) increases. And w ̃ for different λ ∈ (1 2 , 2 3) ultimately tend to λ − 1 3 λ − 1 , the value of which are in the range of (− 1 , − 1 3). Obviously, the expansion of the cosmology filled with radiation and dust or only dust in Rastall gravity (1 2 < λ < 2 3) accelerates without any "exotic" energy whose equation of state w < − 1 3 . [ABSTRACT FROM AUTHOR]

In this paper, we have developed a class of new solutions for relativistic compact stars in higher-dimensional (D ≥ 4) space-time assuming pseudo-spheroidal geometry of the grr metric component. To study the physical properties, we consider equation of state of interior strange matter p = 1 3(ρ − 4B), as proposed in MIT bag model in the presence of a density-dependent B parameter. The interior matter of a quark star may consist of three flavor quarks. We observe some interesting results. The parameter B depends on the anisotropy (α) in the interior, and at the stellar surface, B attains a constant value independent of α. At the interior, B increases with the increase of α. We also note that the value of B approaches a constant value with increasing spheroidal parameter λ. B(ρ) also depends on space-time dimensions and it is interesting to note that B(ρ) picks up negative values near core region which limits the number of space-time dimensions available for a stellar model. All the stability criterion and energy conditions hold good for a physically realistic stellar configuration. It is observed that strange quark matter may be stable or metastable or unstable depending upon the value of energy per baryon (EB). Strange quark matter will be stable if energy per baryon EB < 930.4MeV/fm3. It is noted that the maximum mass obtainable in this model is 1.99M⊙ considering stable strange quark matter when dimension D = 4. In addition, we observe that the dimensions have some effect on the gross properties of strange stars (SS). [ABSTRACT FROM AUTHOR]

In this paper, we investigate the anisotropic and spatially homogeneous Bianchi type-I universe with Kaniadakis holographic dark energy in Saez–Ballester [Phys. Lett. A 113, 467 (1986)] theory of gravitation. We determine Kaniadakis holographic dark energy model by assuming a correlation between the metric potentials to solve the field equations of the model. This results in a dynamical deceleration parameter which demonstrates an accelerating expansion of the universe. Our model’s equation of state parameter ωkhde close to −1 (ΛCDM model) at late-times and is in agreement with the most recent observations. Next, we obtained the squared sound speed (vs2) and found that it is positive, implying stability against perturbations. The ωkhde−ωkhde′ plane is constructed to investigate the evolution of the models’ EoS parameter turned out to be in a freezing zone. As should be the case in an expanding universe, the strong energy conditions of the model are violated. Statefinders (r,s), and r−q planes were also examined. Our model includes the Chaplygin gas, ΛCDM limit, and is inclined towards the steady-state model. [ABSTRACT FROM AUTHOR]

In this paper, we use the cosmographic approach to discuss Friedmann space-time in the presence of torsion. For this, we explore equations of motion that explain creation in an isotropic and homogeneous cosmic backdrop with nonzero torsion. Here, we consider the energy density of holographic dark energy model ρd = 3c2(z)M p2L−2 where c2 is a dimensionless parameter depending on redshift parameter z,Mp = 1 κ is the reduced Planck mass and L represents the holographic length scale. We examine this dark energy model with both constant and variable holographic length scales in terms of Hubble parameter to determine the best-fit scale. The interaction between dark sector components is taken to evaluate cosmographic parameters, like Hubble, equation of state, deceleration, jerk, snap, lerk and statefinder parameters. We consider four c(z) parametrizations, which are Chevallier–Polarski–Linder, Jassal–Bagla–Padmanabhan, Wetterich and Ma–Zhang for both cases. We obtain consistent results for specific choices of constant parameters in the underlying scenario. [ABSTRACT FROM AUTHOR]

This paper is devoted to investigating the behavior of charged compact stars in the f(R,ϕ,X) theory of gravity, where R denotes the Ricci Scalar, ϕ is a scalar potential, and X is a kinetic term. For this purpose, we consider spherically symmetric spacetime with Bardeen geometry as exterior spacetime to investigate various properties of compact stars, including energy density and pressure components. Matching conditions are used to find model parameters. We present a detailed analysis, including a discussion of equations of state parameters, and stability criteria. In this analysis, we discuss the energy conditions to check the viability of our model. Furthermore, an equilibrium condition can be visualized through the modified Tolman–Oppenheimer–Volkov equation. It is concluded that Bardeen’s geometry supports the existence of compact stars in the background of the f(R,ϕ,X) theory of gravity. [ABSTRACT FROM AUTHOR]

The primary objective of this paper is to examine singularity-free solutions within the framework of anisotropic solutions for the Chaplygin equation of state in f (R , ϕ , X) modified gravity theory. Herein, R signifies the Ricci scalar, ϕ denotes the scalar field, and X represents the kinetic term associated with ϕ. The investigation employs the Krori–Barua metric to explore the characteristics of an anisotropic compact star. In the course of our analysis, we specifically consider observational data about three distinct stellar structures: Her X-I, LMC X-4, and 4U 1538-52. Our inquiry extends to the graphical examination of various physical parameters, encompassing energy density, pressure components, anisotropic components, equation of state parameters, equilibrium conditions, stability analysis, adiabatic index, and energy conditions. Furthermore, we delve into the intricacies of the mass-radius function, compactness factor, and surface redshift–integral features of charged compact stars. The culmination of our findings suggests that the f (R , ϕ , X) theory of gravity when subjected to observational scrutiny, manifests as realistic, stable, and devoid of singularities. [ABSTRACT FROM AUTHOR]

In this paper, we have investigated an anisotropic cosmological model in f (Q) gravity with string fluid in LRS Bianchi type-I universe. We have considered the arbitrary function f (Q) = Q + α Q + 2 Λ , where α is model free parameter and Λ is the cosmological constant. We have established a relationship between matter energy density parameter Ω m and dark energy density parameter Ω Λ through Hubble function using constant equation of state parameter ω. We have made observational constraint on the model using χ 2 -test with observed Hubble datasets H (z) and SNe Ia datasets, and obtained the best fit values of cosmological parameters. We have used these best fit values in the result and discussion. We have discussed our result with cosmographic coefficients and found a transit phase dark energy model. Also, we analyzed the Om diagnostic function for anisotropic universe and found that our model is quintessence dark energy model. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the late-time accelerated universe evolution in a flat, homogeneous and isotropic model in the context of f (Q , T) gravity, where Q and T are non-metricity scalar and trace of energy–momentum tensor, respectively. The scale factor, by construction, yields ekpyrotic contraction era followed by a non-singular bounce. The expanding era of the universe yields late-time dark energy era preceded by matter-dominating decelerating era. The model unifies an ekpyrotic, non-singular bounce with the present dark energy-dominated epoch. The model parameters in the functional form of f (Q , T) gravity affect the dynamical evolution of the equation of state (EoS) parameter. The theoretical value of EoS parameter is found to be ω 0 = − 1. 0 1 3 6 , − 1. 0 2 7 3 for n = 0 , 1 , respectively, and it lies in range of the estimated value of EoS parameter from the Planck+SNe+BAO observational data. Different aspects of this bouncing model including behavior of geometrical and physical quantities along with energy conditions have been discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the effects of expansion on large-scale structure formation in our universe. We do that by incorporating a cosmological constant term in the gravitational partition function. This gravitational partition function with a cosmological constant is used for analyzing the thermodynamics of this system. We analyze the virial expansion for this system, and obtain its equation of state. It is observed that the generalization of this equation of state is like the Van der Waals equation. We also analyze a gravitational phase transition in this system using the mean-field theory. We construct the cosmic energy equation for this system of galaxies, and discuss its consequences. We obtain and analyze the distribution function for this system, using the gravitational partition function. We also compare the results obtained in this paper with the observational data. [ABSTRACT FROM AUTHOR]

This paper is devoted to observe the physical attributes of isotropic relativistic spherical objects in the context of Rastall theory of gravity. In order to inspect the structural composition of spherical objects, the Tolman IV solution is taken into account. The unknown parameters associated with Tolman IV solution are evaluated through matching conditions with derived values of radii and masses of some specific star models. The consistency of the adopted ansatz is analyzed via graphical interpretation of matter variables, equation of state parameter, mass components, energy constraints, causality condition and stellar equation for several choices of Rastall parameter. It is observed that the considered solution does not admit singularities in the matter variables. Moreover, in accordance with the graphical analysis, the stellar models satisfy all physical requirements anticipated in a realistic star. It is also shown that for vanishing Rastall coupling parameter, the standard outcomes of general relativity can be retrieved. [ABSTRACT FROM AUTHOR]

This paper is devoted to study FRW universe in the context of Chern–Simons corrected f (R) gravity. In particular, the work provides the investigation of cosmological dynamics within modified gravity by assuming a suitable Hubble parameter that might result in a realistic bouncing universe. For this purpose, we consider a suitable Hubble parameter and examine the bouncing cosmology by assuming a well-known f (R) gravity model. Further, we explore the behavior of energy density and pressure profiles by employing the chosen Hubble parameter. We obtain positive and increasing trends of energy density during the bouncing phase while the negative behavior of pressure in our work could potentially be associated with cosmic expansion. We have also studied the energy conditions and in our case NEC is not violated perhaps due to the reason that the equation of state parameter is not crossing the phantom divide. However, the SEC is violated justifying a successful bounce. Moreover, the validation of DEC and TEC suggests that the chosen model is well behaved in nature. The Hubble parameter passing through the bouncing point shows an increasing trend, indicating an expansion phase after the bounce. The equation of state parameter is negative after the bouncing spot, particularly around ω ≈ − 1. This behavior justifies the current cosmic expansion. The deceleration parameter exhibits a negative behavior implies that the cosmological model demonstrates cosmic expansion. Thus all the results validate the existence of a bouncing universe with the chosen model in Chern–Simons corrected f (R) gravity. [ABSTRACT FROM AUTHOR]

The aim of this paper is to examine the singularity-free solutions for anisotropic stellar structures in f (R , ϕ) theory of gravity, where R denotes the Ricci scalar and ϕ represents the scalar field. For this purpose, we consider the spherically symmetric spacetime to discuss the stellar structures with anisotropic fluid. Moreover, the Einstein field equations are solved by using Chaplygin equation of state, and the Karori–Barua metric. To analyze the charged stellar structure, we use the matching conditions of spherically symmetric spacetime with the Reissner–Nordstrom exterior metric and develop some expressions for finding the unknown parameters. We further investigate the graphical behavior of energy density, pressure components, anisotropic component, equation of state parameters, equilibrium condition, stability analysis, adiabatic index and energy conditions. Conclusively, our considered stellar structures under observations are realistic, stable, and are free from any singularities. [ABSTRACT FROM AUTHOR]

In this paper, the basic Einstein–Hilbert cosmological model is extended by adding a new functional F (G , T μ ν T μ ν) in the fundamental action, encoding specific geometrical effects due to a nontrivial coupling with the Gauss–Bonnet invariant (G), and the energy–momentum squared term ( T μ ν T μ ν ). After obtaining the corresponding gravitational field equations for the specific decomposition where F (G , T μ ν T μ ν) = f (G) + g (T μ ν T μ ν) , we have explored the physical features of the cosmological model by considering the linear stability theory, an important analytical tool in the cosmological theory which can reveal the dynamical characteristics of the phase space. The analytical exploration of the corresponding phase space structure revealed that the present model can represent a viable dark energy model, with various stationary points where the effective equation of state corresponds to a de-Sitter epoch, possible explaining the early and late time acceleration of the Universe. [ABSTRACT FROM AUTHOR]

In this paper, we consider the framework of the newly proposed modified theory of gravity named f (R , A) gravity, wherein R and A signify the Ricci and anticurvature scalars, respectively. For our cosmic discussions, we evaluate a renowned f (R , A) model, incorporating various forms of the scale factor within the context of Friedmann–Robertson–Walker (FRW) spacetime. Our exploration delves into energy conditions, the effective equation of state parameter and the stability of models within the f (R , A) theory. These models are further elucidated through graphical representations plotted against time and their respective model constants. Notably, it is observed that scale factors with exponential terms yield more consistent results in comparison to those of power-law forms, given specific values of model constants. [ABSTRACT FROM AUTHOR]

In this paper, we inspect the stable geometry of thin-shell wormholes in the background of static spherically-symmetric AdS black holes solution bounded by dark fluid and Chaplygin-like equation of state p = − ℬ / ρ , where p and ρ denote the pressure and energy density that are related through positive constant ℬ. For this purpose, we consider the two equivalent copies of black holes and connected them at the hypersurface through cut and paste approach. Then, we employ the linearized radial perturbation to discuss the stability of the developed wormhole geometry by assuming variable equations of state. We obtain the maximum stable configuration for massive black holes for both barotropic and Chaplygin variable equations of state while for higher values of n , stable regions decrease. It is found that for every selection of physical parameters of black hole geometry with low intensity of Chaplygin dark fluid, we get the stable configuration of thin-shell wormholes. [ABSTRACT FROM AUTHOR]

This paper explores the effects of cloud of strings and quintessence on the thermodynamic features of the 4D Einstein–Gauss–Bonnet (EGB) Black Hole (BH). For this purpose, we have evaluated temperature, entropy, Gibb's free energy and heat capacity of the 4D EGB BH in the presence of cloud of strings and quintessence. We have also shown the graphical behavior of all these physical quantities for various values of Gauss–Bonnet term α , quintessence q , equation of state parameter w and cloud of string a = 0 , 1 , 2 , 3. [ABSTRACT FROM AUTHOR]

In this paper, we study a flat homogeneous FLRW model in Lyra geometry which is described by a time-dependent displacement vector. We consider an appropriate parametrization of the energy density of scalar field ρ ϕ in terms of the cosmic scale factor. The result shows two transitions from deceleration to acceleration. Furthermore, we constrain the model parameter α and the displacement field vector β using the recent supernovae data, Hubble dataset of 77 points and their joint data which predict the accelerated expanding phase of the universe in late times. The effective equation of state parameter ω eff speculates Λ CDM in late times. Finally, we use the statefinder diagnostic to differentiate our model from the various dark energy models. [ABSTRACT FROM AUTHOR]

Holographic dark energy (HDE) models are significantly different from standard dark energy (DE) models since they are based on holographic principles rather than mentioning a term in Lagrangian. Nojiri et al. [Barrow entropic dark energy: A member of generalized holographic dark energy family, Phys. Lett. B 825 (2022) 136844] proposed a generalized Barrow HDE (BHDE) model depending on particle horizon and future horizon, where the infra-red cut-off is considered as a usual cut-off. In this paper, we have revisited the generalized BHDE adopting the Granda–Oliver cut-off as the standard cut-off for the model. We have generalized BHDE behaviors with two different cut-offs, future horizon L f and particle horizon L p . The holographic cut-off is extended to depend on L GO = L GO (L p , L ̇ p , L ̈ p , ... , L f , L ̇ f , ... , a) , where a is the scale factor. Using this formalism, we demonstrated that the Barrow entropic DE model is equivalent to the generalized HDE model, where two ways are used to compute the respective holographic cut-off: first, in terms of particle horizon and its derivative, and second, future horizon and its derivative. We use 57 observational data points to determine the current Hubble constant H 0 . We have studied the behavior of few quantities, such as DE density (ρ de ) , pressure (p de ) , equation of state (EoS) parameter under the observational data. Here, we have to find the EoS parameter for generalized HDE, equivalent to Barrow entropic DE model. Besides this, we have also discussed k-essence and tachyon DE models. [ABSTRACT FROM AUTHOR]

In this paper, we have explored the field equations of f (T , B) gravity as an extension of teleparallel gravity in an isotropic and homogeneous space-time. In the basic formalism developed, the dynamical parameters are derived by incorporating the power law and exponential scale factor function. The models show accelerating behavior and approach Λ CDM at late time. The present value of the equation of state parameter for both the cases is obtained to be in accordance with the range provided by cosmological observations. The geometrical parameters and the scalar field reconstruction are performed to assess the viability of a late-time accelerating universe. Further, the stability of both the models is presented. It has been observed that both the models are parameter-dependent. Since most of the geometrically modified theories of gravity favor the violation of strong energy condition (SEC), we have derived the energy conditions both for the power law and exponential model. In both the models, the violation of SEC is established. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the dynamic evolution of universe in the models of holographic dark energy with f (Q , T) gravity framework where, Q is the non-metricity scalar and T is the energy–momentum tensor trace. We have considered f (Q , T) = α Q + β T framework and investigated the evolution of cosmological quantities like energy density, equation of state (EoS) parameter and classical stability parameter with redshift. We parameterize the deceleration parameter and confront the Hubble parameter with the observational data. We investigate for the late-time accelerated expansion of universe and discuss the stability of the model by using adiabatic sound speed squared parameter. A comparison among these derived models suggest that the Renyi holographic dark energy model with GO cutoff satisfies the observational constraint of Planck+SNe+BAO on EoS parameter at present time as compared to other models. Diagnostic tools such as Statefinders and Om diagnostic have been used to classify the dark energy evolution regions. [ABSTRACT FROM AUTHOR]

In this paper, we have studied Kaluza–Klein Cosmological Model with strange-quark-matter in Lyra Geometry. To determine the solution of the field equation, we have assumed that scalar expansion is proportional to shear scalar σ 2 which leads to A 1 = (A 2) r , where A 1 , A 2 are metric potentials and r is arbitrary constant. The cosmological parameters are investigated with the help of equation of state strange-quark-matter (SQM), which is p = ρ − 4 B c 3 , where B c is Bag constant. We compared the results of general General relativity (GR) and scalar-tensor theory and also discussed the behaviors of some physical parameters. [ABSTRACT FROM AUTHOR]

This paper inspects the impact of minimal matter-geometry coupling present in R + α R 2 + γ T model of f (R , T) theory on the physical attributes of anisotropic quark stars. The geometry of considered stellar candidates is modeled via spherically symmetric static spacetime whose metric functions are influenced by Heintzmann solutions. The inner matter distribution of the stellar system is assumed as anisotropic with the phenomenological MIT bag model equation of state. The expressions of unknown parameters that appear in Heintzmann solution are evaluated in terms of mass and radius by the continuity of interior and exterior geometries. Further, insertion of masses and radii of some particular observed stellar models will yield their numerical values. In order to discuss the physical acceptability as well as stability of the quarks stars based on the considered solutions, we have checked the physical behavior of matter variables, mass and related quantities, energy conditions, equilibrium of forces, adiabatic index and Herrera's cracking concept. The energy conditions are fulfilled ensuring the compatibility of assumed matter and geometry of quark stars. It is also found that all compact star candidates exhibit stable structures corresponding to the proposed values of the model parameters. Hence, the considered f (R , T) model shows consistency with all the physical conditions and presents a viable study to the nature of anisotropic massive stellar system. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to examine the anisotropic matter distribution concerning one of the well-known f (R , T) theories of gravity, where R and T represent the Ricci scalar and trace of the energy–momentum tensor, respectively. We consider anisotropic matter distribution in spherically symmetric spacetime for our desired work. We investigate the physical behavior of pressure components, energy density, anisotropic function, equation of state parameters, and energy conditions. Furthermore, we analyze the stability of compact stars by investigating the causality condition, adiabatic index, and generalized Tolman–Oppenheimer–Volkoff equation. Some fundamental features of compact stars have been investigated, like compactness factor, mass function, and surface redshift. Our calculated solutions for Bardeen stellar structures are consistent and stable in the background of the f (R , T) theory of gravity. [ABSTRACT FROM AUTHOR]

In this paper, we investigate spherically symmetric gravitational collapse of thick matter shell without radiation in the Einstein gravity with cosmological constant. The orbit of the infalling thick matter is determined by imposing an equation of state for the matter near interface, where pressure constituted of the transverse component and the longitudinal one is proportional to energy density. We present analytic solutions for the equation of state and discuss parameter region to satisfy physical conditions such as the absence of the shell crossing singularity, the monotonic increase of the emergent infinite redshift surface and energy conditions. We finally show that adopting the definition presented in arXiv:2005.13233 the total energy in this time-dependent system is invariant under the given time evolution. [ABSTRACT FROM AUTHOR]

In this paper, the higher-dimensional collapse of homogeneous isotropic perfect fluid is studied by considering the geometry of five-dimensional spherically symmetric metric. Using equations of state for different fields like dust, radiation and stiff fluid with and without cosmological constant Λ , the gravitational collapse is studied. The results are compared with the usual four-dimensional study in [A. V. Astashenok, K. Mosani, S. D. Odintsov and G. C. Samanta, Int. J. Geom. Methods Mod. Phys. 16, 1950035 (2019)]. It is found that the collapse rate is faster in five-dimensional spacetime as compared to four-dimensional case supporting the cosmic censorship hypothesis. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the cosmic analysis of Kaniadakis holographic dark energy model in the frameworks of f (G) and f ̃ (T) modified theories of gravity. We reconstruct functional forms of f (G) and f ̃ (T) models by using a well-known power-law form of scale factor and flat FRW metric. The behavior of these functional forms with respect to their arguments is discussed. Using these models, various cosmic parameters like energy conditions, effective equation of state parameter, deceleration parameter and squared speed of sound parameters are explored to discuss the accelerated expansion of the universe. We obtain some consistent results for accelerated expansion of the universe related to specific values of model parameters. [ABSTRACT FROM AUTHOR]

In this paper, we show how the Gambier equation arises in connection to Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology and a Dark Matter equation of state. Moreover, we provide a correspondence between the Friedmann equations and the Gambier equations that possess the Painlevé property in (2 + 1) dimensions. We also consider special cases of the Gambier G27 equation such as the generalized Pinney equation. For an extended FLRW model with dynamic scalar field as matter model, the Einstein equations correspond to the Milne–Pinney equation which in turn can be mapped to the parametric Gambier equation of second order. [ABSTRACT FROM AUTHOR]

The main emphasis of this paper is to find the viable solutions of Einstein Maxwell field equations of compact star in context of modified f (R) theory of gravity. Two different models of modified f (R) gravity are considered. In particular, we choose isotropic matter distribution and Bardeen's model for compact star to find the boundary conditions as an exterior space-time geometry. We use the conformal Killing geometry to compute the metric potentials. We discuss the behavior of energy density and pressure distribution for both models. Moreover, we analyze different physical properties such as behavior of energy density and pressure, equilibrium conditions, equation of state parameters, causality conditions and adiabatic index. It is noticed that both f (R) gravity models are suitable and provide viable results with Bardeen geometry. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing interest in stellar modeling in the framework of Einstein–Gauss–Bonnet gravity. In this paper, for a relativistic star in static equilibrium, we invoke the five-dimensional Einstein–Gauss–Bonnet gravity and solve the system by assuming a matter distribution that admits a linear equation of state. We fix the model parameters by matching the interior solution to the exterior Boulware–Deser metric, which facilitates physical analysis of the resultant configuration. We analyze the star's gross physical properties, which brings to attention the role of the Gauss–Bonnet coupling parameter α in fine-tuning the values of the matter variables. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the Rényi holographic dark energy model with the interaction between dark energy and dark matter within the framework of the fractal cosmology in which the Hubble horizon is considered as the IR cutoff. In this setting, we derive the evolution equation of the Rényi holographic dark energy density parameter, the equation of state (EoS) parameter and deceleration parameter. We find that the model in the fractal cosmology can explain the accelerated expansion of the universe. In addition, we discuss the statefinder diagnosis of this model, plotting the curves of r and s with redshift z and the evolutionary trajectories of r − s. We find that statefinder can ideally break the degeneracy of different coupling parameter values in this model. Moreover, we find that the statefinder pair S 3 (2) performs better than S 3 (1) and r − s in this model. [ABSTRACT FROM AUTHOR]

In this paper, we explore the wormhole solutions (which are initially proposed by R. Garattini [Eur. Phys. J. C 79 (2019) 951] who take generalized uncertainty principle (GUP) with Casimir energy) in the framework of two well-known dark energy (DE) models, generalized Chaplygin gas (GCG) and polytropic gas. We consider the GUP corrected pressure (force per unit surface area) in the equation of state (EoS) of these DE models to construct the GCG corrected energy density and polytropic gas corrected energy density. Three models of redshift function are taken into account to construct shape function as well as wormhole geometry for both cases of corrected energy densities. We find the behavior of EoS parameters, redshift function for isotropic and anisotropic fluid, equilibrium conditions, null energy condition and exotic volume at the throat of the wormhole with radius r 0 . [ABSTRACT FROM AUTHOR]

In this paper, we study an isotropic and homogeneous Friedmann–Lemaitre–Robertson–Walker cosmological model in Weyl type f (Q , T) gravity with a dynamic deceleration parameter. The solution of the field equations is found using a variable deceleration parameter, viz., q = n + m H , with q the deceleration parameter, n and m constants, and H the Hubble parameter [Tiwari et al., Eur. Phys. J. Plus 132, 1 (2017)]. Then we calculate the values of the model parameters that are most likely to accord with the most recent observational data sets. We make use of the 57 CC points, SN and BAO datasets. We have contracted a graphical representation of the dynamical behavior of the cosmological parameters (the Hubble parameter, the deceleration parameter, the energy density and the equation of state) in terms of the redshift. To investigate the various eras of the universe, the evolution of the statefinder trajectory pairs (s , r) and (q , r) are studied. It is shown that the main energy component of the model is ordinary matter, which behaves initially as the SCDM model and then later as a fluid resembling quintessence, which behaves as the well-known Λ CDM model. A suitable cosmological model is constructed after analyzing the physical parameters of the model, the O m (z) diagnostic analysis. [ABSTRACT FROM AUTHOR]

In this paper, we consider two modified Chevallier–Polarski–Linder (CPL) models in the background of homogeneous and isotropic FLRW space-time model. From the observational dataset (Pantheon + BAO + HST) we find that the logarithmic form of the equation of state for the dark energy (model II) is more preferred with the use of AIC and BIC and tightly constrained than the other form of the equation of state parameter (model I). However, model I is more favored compared to the model II in the context of Bayesian evidence. Finally, for H 0 tension it is found that model I is more preferable than model II. [ABSTRACT FROM AUTHOR]

In this paper, we obtain a new class of stationary axisymmetric spacetimes by using the Gürses–Gürsey metric with an appropriate mass function in order to generate a rotating core of matter that may be smoothly matched to the exterior Kerr metric. The same stationary spacetimes may be obtained by applying a slightly modified version of the Newman–Janis algorithm to a nonrotating spherically symmetric seed metric. The starting spherically symmetric configuration represents a nonisotropic de Sitter-type fluid whose radial pressure p r satisfies an state equation of the form p r = − ρ , where the energy density ρ is chosen to be the Tolman-type-VII energy density [R. C. Tolman, Phys. Rev.55, 364 (1939)]. The resulting rotating metric is then smoothly matched to the exterior Kerr metric, and the main properties of the obtained geometries are investigated. All the solutions considered in this study are regular in the sense they are free of curvature singularities. Depending on the relative values of the total mass m and rotation parameter a, the resulting stationary spacetimes represent different kinds of rotating compact objects such as regular black holes, extremal regular black holes, and regular starlike configurations. [ABSTRACT FROM AUTHOR]

The imprint of interacting dark energy (IDE) needs to be correctly identified in order to avoid bias in constraints on IDE. This paper investigates the large-scale imprint of IDE in redshift-space distortions (RSDs), using Euclid-like photometric prescriptions. A first attempt at incorporating the IDE dynamics in the galaxy (clustering and evolution) biases is made. Without IDE dynamics taken into account in the galaxy biases, as is conventionally done, the results suggest that for a constant dark energy (DE) equation of state parameter, an IDE model where the DE transfer rate is proportional to the DE density exhibits an alternating, positive–negative effect in the RSDs angular power spectrum. However, when the IDE dynamics is incorporated in the galaxy biases, it is found that the apparent positive–negative alternating effect vanishes: implying that neglecting IDE dynamics in the galaxy biases can result in "artifacts" that can lead to incorrect identification of the IDE imprint. In general, the results show that multi-tracer analysis will be needed to beat down cosmic variance in order for the RSDs angular power spectrum as a statistic to be a viable diagnostic of IDE. Moreover, it is found that RSDs hold the potential to constrain IDE on large scales, at redshifts z ≤ 1 , with the scenario having IDE dynamics incorporated in the biases showing better potential. [ABSTRACT FROM AUTHOR]

In this paper, we study the Chaplygin gas equation in curvature-matter coupling gravity to describe the observed expansion of the universe. We consider the Chaplygin gas equation of state in terms of the energy density ρ and pressure p , by the relationship p = − A ρ and the curvature-matter coupling gravity as f (R , T) , where A is a positive constant, R and T denote, respectively, the Ricci scalar and the trace of energy–momentum tensor. Considering the gravitational lagrangian in the form f (R , T) = R + h (T) , where we used two forms of h (T) and by assuming a perfect fluid as matter source, we determined through the modified Friedmann equations, the corresponding energy and pressure for each model. By using the free parameters of our models, we performed the numerical results of the energy conditions to study its viability. Furthermore, we have derived some cosmological parameters like deceleration parameter and statefinder parameters and graphically investigated the nature of these parameters in Chaplygin gas model. [ABSTRACT FROM AUTHOR]

Steering is a type of nonseparable quantum correlation, where its inherent asymmetric feature makes it distinct from Bell nonlocality and entanglement. In this paper, we investigate quantum steering in a two-mode Gaussian state ϱ ̂ c 1 c 2 coupled to a two-mode vacuum reservoir. The mode c 1  ( c 2 ) is emitted during the first (second) transition of a nondegenerate three-level cascade laser. By means of the master equation of the state ϱ ̂ c 1 c 2 , we derive the analytical expression of the steady-state covariance matrix of the modes c 1 and c 2 . Using realistic experimental parameters, we show that the state ϱ ̂ c 1 c 2 can exhibit asymmetric steering. Furthermore, by an appropriate choice of the physical parameters of the state ϱ ̂ c 1 c 2 , we show that one-way steering can be achieved. Essentially, we demonstrate that one-way steering can, in general, occur only from c 1 → c 2 . Besides, we perform a comparative study between the steering of the two laser modes and their Gaussian Rényi-2 entanglement. As a result, we found that the entanglement and steering behave similarly in the same circumstances, i.e. both of them decay under dissipation effect; moreover, they can be well enhanced by inducing more and more quantum coherence in the state ϱ ̂ c 1 c 2 . In particular, we found that the steering remains always less than the Gaussian Rényi-2 entanglement. [ABSTRACT FROM AUTHOR]

By constructing models of quark stars (QSs), we use the MIT bag model as a strange quark matter equation of state (EoS). According to the strange matter hypothesis, the MIT bag model is the most successful phenomenological models of quarks confined to hadrons. This paper aims to explore the internal structure and the physical properties of QSs in the context of four-dimensional (4D) Einstein–Gauss–Bonnet (EGB) theory of gravity. The main feature of 4D EGB theory is that there is a nontrivial contribution to the gravitational dynamics in 4D spacetime. We present the essential features of QSs concerning the mass-radius relation depending on the interplay of matter parameters and the GB coupling constant. Our results show that all studied cases are found to be consistent with observations and physically relevant. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the feasibility and the appearance of charged thin-shell wormholes using generalized Chaplygin gas under the influence of minimally coupled f (R , T) gravitational theory. Here, f is a generic function of the scalar curvature R and the trace of stress-energy tensor T. We explore different components of Lanczos equations in the context of a specific f (R , T) functional form, i.e. f (R , T) = R + 2 λ T , by applying junction conditions on field equations. We study static stable solutions using radial perturbation and the generalized Chaplygin gas equation of state (EoS) with the isotropic environment. We investigate the stable (unstable) static wormhole solutions for various physical parametric values and illustrate them graphically. [ABSTRACT FROM AUTHOR]

In this paper, we explore the homogeneous and isotropic flat Friedmann–Robertson–Walker (FRW) model in Chameleon cosmology. By considering a non-minimal coupling between the scalar field and matter, we present a non-singular bouncing cosmological scenario of the universe. The universe initially exhibits the ekpyrotic phase during the contracting era, undergoes a non-singular bounce, and then in expanding era, it smoothly transits to the decelerating era having matter and radiation-dominated phases. Further, this decelerating era is smoothly connected to the late-time dark energy-dominated era of the present epoch. We use numerical solution techniques to solve non-minimally coupled gravity equations for understanding the evolution of scalar field along with other quantities like effective potential in the model. The model thus unifies an ekpyrotic, non-singular, asymmetric bounce with the dark energy era of the present epoch. We study the evolution of bouncing model and confront the model with observational results on the equation of state parameter by constraining the model parameters. [ABSTRACT FROM AUTHOR]