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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 explore the existence of wormholes in the context of f (R , T) gravity. The f (R , T) theory is a curvature-matter coupled modified gravity that depends on an arbitrary function of the Ricci scalar R and the trace of the stress-energy tensor T. In this work, we adopt two different choices for the matter Lagrangian density ( ℒ m = and ℒ m = p r ) and investigate the impact of each one on wormhole structure. By adequately specifying the redshift function and the shape function, we found a variety of exact wormhole solutions in the theory. Our finding indicates that for both classes of wormholes, the energy density is always positive throughout the spacetime, while the radial pressure is negative. This means exotic matter is necessary for the existence of wormholes in f (R , T) gravity. [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]

The construction of compact star models with quintessence and cloud of strings anisotropic fluid lays the foundation for the research presented in this paper, which focuses on the ansatz of f(Q) gravity. We utilized a spherically symmetric spacetime to derive the field equations incorporating quintessence and cloud of strings anisotropic matter fields. The well-known Karmarkar condition was employed to obtain the gravitational components of the spherically symmetric spacetime. The constant parameters used in the study were obtained by applying junction conditions on the interior and exterior spacetimes. We used the mass and radius of P S R J 1 6 1 4 − 2 2 3 0 & S M C X − 1 , which are already present in the literature. Afterward, we calculated the important properties of quintessence stars in the presence of cloud of strings to ensure the stability and physical presence of compact models. To achieve this goal, we studied features such as energy density, quintessence density, pressure profiles, gradients, anisotropic factor, energy conditions, sound speeds, TOV forces, EoS components, mass function, compactification and redshift. [ABSTRACT FROM AUTHOR]

This paper explores the dynamic behavior of the universe within the framework of the f (R , G) theory of gravity. Here, R and G represent the Ricci scalar and Gauss–Bonnet invariant, respectively. By solving the modified field equations with the chosen f (R , G) function, specifically f (R , G) = R + m R 2 + n G 2 , we determine the best fit values of model parameters that are consistent with recent observational datasets. These datasets include 57 data points from the Cosmic Chronometers, Pantheon, and BAO datasets. Furthermore, we analyze the physical properties of cosmographic parameters, such as energy density and pressure, corresponding to the constrained values of the model parameters. The evolution of the deceleration parameter in our study indicates a transition from a decelerated phase to an accelerated phase in the universe. Remarkably, our f (R , G) cosmological model effectively describes the late-time cosmic acceleration without requiring the introduction of a dark energy component in the field equations. [ABSTRACT FROM AUTHOR]

In this paper, we explore the physical properties and characteristics of static, spherically symmetric wormholes in the background of Rastall–Rainbow gravity. The Rastall–Rainbow gravity theory has recently been proposed as a combination of two theories, namely, the Rastall theory and the Rainbow description. We implemented noncommutativity by adopting two different distributions of energy density (Gaussian and Lorentzian) in the Morris and Thorne metric. We solve the field equations analytically and discuss all the properties of wormholes depending on the two model parameters. Notably, for specific parameter ranges, one can alleviate the violation of the WEC at the throat and its neighborhood. [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]

In this paper, we investigate the dynamical behavior of the universe with a flat FLRW model in f (R , G) gravity, where R and G both signify the Ricci scalar and Gauss–Bonnet invariant. Furthermore, in order to determine the model's behavior, it must have the late-time universe's behavior, which involves both an accelerated expansion as well as ending in a big rip. We present a model that begins with a point-type singularity, i.e. a point with zero volume and infinite energy density, by using parametrization of the scale factor a (t). The model's actions are accelerating and expanding at the moment, and Λ CDM in late times. Our extensive analysis encompasses the energy conditions, dynamics of certain model solutions and additional cosmological tests through a dominant model. Finally, the proposed framework acts exactly like a quintessence dark energy model in the current time and is reliable with standard cosmology Λ CDM in late times. [ABSTRACT FROM AUTHOR]

This paper proposes a new framework to investigate the spherically symmetric of anisotropic stars with clouds of strings and quintessence field in Rastall gravity. We develop the field equations in a spherically symmetric space–time with a quintessence field and clouds of string. We utilize the mass and radius of Her X-1, Vela X-1, SMC X-1, SAX J1808 0.4-3658 and 4 U 1538-52, which are well mentioned in the literature. We applied the matching conditions by considering outer space calculated in Rastall gravity to evaluate the constants parameters. To check the stability and physical presence of compact models, we computed the most important features of quintessence stars in the presence of a cloud of strings. We explored characteristics including energy density, quintessence density, radial pressure, tangential pressure gradients, anisotropic factor, energy conditions, sound speeds, TOV forces, EoS components, mass function, compactification and redshift. [ABSTRACT FROM AUTHOR]

This paper aims to conduct an extensive examination of hyperbolically symmetrical static fluid distributions, wherein a precise analysis of their physical characteristics is carried out in the background of modified f (G , T) gravity, where G and T stands for Gauss Bonnet invariant and energy-momentum trace, respectively. The outcomes reveal that the energy density exhibits negative value, thus implying that any utilization of such fluids necessitates extremely demanding circumstances where quantum effects would be significantly influential. Furthermore, it has been determined that these fluid distributions cannot take the vicinity surrounding their central point of symmetry and leave behind an empty vacuum cavity in its place. Additionally, an appropriate definition for mass function and the complexity factor is determined. Eventually, we exhibit a broad strategy for accomplishing particular solutions and showcase several instances of exact analytical solutions in the presence of f (G , T) correction terms. [ABSTRACT FROM AUTHOR]

The primary goal of this paper is to examine spacetimes admitting semiconformal curvature tensor in f (ℛ) modify gravity. The semiconformal flatness of general spacetime and spacetime in f (ℛ) gravity with perfect fluid, has been analyzed. For this consideration, we generate the forms of isotropic pressure p and energy density σ. After that, a few energy conditions are taken into account. Finally, we study the divergence-free semiconformal curvature tensor in f (ℛ) gravity in presence of perfect fluid. We emphasize that for recurrent or bi-recurrent energy–momentum tensor, Ricci tensor of this spacetime is semi-symmetric and consequently, the resulting spacetimes either accomplish inflation or possess fixed isotropic pressure and energy density. [ABSTRACT FROM AUTHOR]

In recent years, a class of compact objects called gravastars have drawn immense interest as regular solutions to end state stellar collapse. Since the energy density involved in collapse process is expected to be high, it is a natural choice to study such compact objects in context of modified gravity theories which reduce to General Relativity (GR) in the low energy regime. We have already framed a model of gravastar in such a modified gravity framework involving extra dimensional Randall–Sundrum (RS) single brane gravity [R. Sengupta, S. Ghosh, S. Ray, B. Mishra and S. K. Tripathy, Phys. Rev. D 102, 024037 (2020)]. As a sequel in this paper, we substantially improve our previous model by choosing the Kuchowicz function as one of the metric potentials, which leads to many new interesting results and physical features from our analysis as discussed in this paper. Also, we provide essential additional stability checks on our gravastar model to investigate the possibility of any instability creeping in due to the higher-dimensional framework. Our present improved gravastar model is found to clear all the stability checks successfully. Very interestingly, the static spherically symmetric matter distributions are found to accommodate both classes of solutions obeying and violating the modified energy conditions on the RS brane as we find in this work. We can conclude from our analysis that the Kuchowicz metric potential is very effective for describing regular solutions to compact objects at substantially high energies on the three-brane. [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 calculate a new class of wormhole solutions in the framework of teleparallel gravity. To obtain a characteristic wormhole solution, we use anisotropic matter distribution and a specific form of two dark matter profiles (URC profile and Quantum wave dark matter). As a general strategy, we create a relationship between calculated energy density and dark matter profiles for the system and investigate the physical properties of the wormhole geometry. A detailed analytical and graphical explanation of the matter contents via energy conditions is provided. The calculated shape functions of wormhole geometry meet the required conditions in both circumstances. Several intriguing features have emerged from the investigation, as have the properties of the exotic matter within the wormhole geometry. Finally, we have concluding remarks. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the conformal vector fields (CVFs) of static cylindrically symmetric (SCS) spacetimes in f (T , B) gravity, a novel modified teleparallel gravity that connects both f (T) and f (R) theories via a boundary term B. Initially, we employ an algebraic approach to extract some classes that represent SCS solutions in f (T , B) gravity. Applying the above-mentioned approach, we find solutions in nine cases. We also investigate the CVFs using the direct integration technique. Following a thorough investigation, we discover that the spacetimes admit proper CVFs in only one case. In rest of the eight cases, the spacetimes either become conformally flat or they admit homothetic vector fields (HVFs) or Killing vector fields (KVFs). The overall dimension of CVFs for the spacetimes under consideration has come out to be 5, 6 or 15. To complete the study, we also compute the energy density and pressure of each model. Corresponding to the resulting models, we discuss the energy conditions in order to check the physical sound of the solutions. [ABSTRACT FROM AUTHOR]

This paper explores collapsing solutions of the field equations in the context of 4D Einstein–Gauss–Bonnet (EGB) gravity. We study the effects of GB-term on the energy density, pressure (tangential and radial) and anisotropy of the collapsing system. We consider expansion scalar (Θ < 0) to obtain the collapsing solution. Furthermore, we discuss the graphical behavior of the source variables. [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, the Morris–Thorne wormholes are studied in the background of f (R , T) = R + α R 2 + β ln T gravity, where α and β are constants. The wormhole solutions are derived in two cases with different assumptions for the matter forms. In each case, the null energy condition (NEC) is analyzed and the range of parameters satisfying the NEC are determined. Further, the stability of solutions is examined with the help of the generalized Tolman–Oppenheimer–Volkoff (TOV) equation. [ABSTRACT FROM AUTHOR]

The treatment of (1+3)-covariant perturbation in a multifluid cosmology with the consideration of f (G) gravity, G being the Gauss–Bonnet term, is done in this paper. We define a set of covariant and gauge-invariant variables to describe density, velocity and entropy perturbations for both the total matter and component fluids. We then use different techniques such as scalar decomposition, harmonic decomposition, quasi-static approximation together with the redshift transformation to get simplified perturbation equations for analysis. We then discuss a number of interesting applications like the case where the universe is filled with a mixture of radiation and Gauss–Bonnet fluids as well as dust with Gauss–Bonnet fluids for both short- and long-wavelength limits. Considering polynomial f (G) model, we get numerical solutions of energy density perturbations and show that they decay with increase in redshift. This feature shows that under f (G) gravity, specifically under the considered f (G) model, one expects that the formation of the structure in the late Universe is enhanced. [ABSTRACT FROM AUTHOR]

There are a number of different theories which tend to explain the concept of universe's accelerated expansion. Among these theories, modified gravity is the most promising one. This paper elaborates matter distribution along with different characteristics of anisotropic compact stars in f (R , G) gravity background. Specifically, to profoundly understand physical behavior of the compact stars, we considered six compact stars, namely: Her X-1 ( CS 1 ), SAXJ1808.4-3658 ( CS 2 ), 4U1820-30 ( CS 3 ), PSR J 1614 2230 ( CS 4 ), VELA X-1 ( CS 5 ) and Cen X-3 ( CS 6 ) and calculated the corresponding quantities such as energy density (ρ), radial pressure ( p r ) and tangential pressure ( p t ) using three distinct models of f (R , G) gravity. For simplicity, f (R , G) gravity is divided into two parts as: f (R , G) = f 1 (R) + f 2 (G). The first part f 1 (R) is considered Hu–Sawicki like model, while the second part f 2 (G) is considered logarithmic like for Model 1 and power law like for Model 2 and Model 3. Predominantly, measurements of anisotropy, the energy conditions (ECs) and stability aspects of models for considered compacts stars are presented using graphical techniques. Furthermore, we also established that for the f (G) model parameter (n > 0), all the six stars show conventional behavior. [ABSTRACT FROM AUTHOR]

Employing the Palatini version of f (R) gravity theory (R being the Ricci scalar), this paper describes the evolution of a radiating axially symmetric fluid and its changeover to a non-radiating state. Orthonormal tetrad formalism is taken into account because this technique is easier to use and yields simple tensors leaving the predictions of the theory unchanged. Effective tetrad components of the heat flux, the vorticity vector and the shear tensor are evaluated along with the two parts (electric and magnetic) of Weyl curvature tensor. Furthermore, certain structure scalars are procured from the orthogonal division of the Riemann tensor to figure out basic characteristics of the fluid source like the energy density, stress anisotropy and the heat flux. Few differential equations are worked out to gain insight into the consistency of modified field equations while the system transits from its radiating to equilibrium state. [ABSTRACT FROM AUTHOR]

In this paper, we study the accretion process of a charged black hole in the background of cloud of strings in the framework of 4D Einstein–Gauss–Bonnet (EGB) gravity theory. Firstly, the steady spherical accretion process of ideal fluid on 4D cloud of strings EGB black hole is studied from the aspects of the radial velocity, the energy density, the mass accretion rate and the sound speed. Then, the general analytical expressions of the accretion process are determined, and the effects of the black hole parameters on the radial velocity, the energy density, the mass accretion rate and the sound velocity are discussed. When the GB coupling constant increases, the energy density and mass accretion rate increase, and the sound velocity and radial speed decrease. EGB gravity and charge have similar physical effects on the accretion process of black hole. [ABSTRACT FROM AUTHOR]

This paper explores the aspects of compact stars in f (T ,) gravity, where T and express the torsion and trace of the energy–momentum tensor. To achieve this goal, we consider a spherically symmetric spacetime with an anisotropic source of fluid. In particular, the Krori–Barua (KB) spacetime is considered to explore the solution of compact stars. In addition, we select three specific types of compact stars models, namely J1416-2230, 4U 1608-52 and Cen X-3. We develop the field equations using the KB spacetime with some specific form of f (T ,) gravity. In addition, we consider the Schwarzschild geometry for the matching conditions at the boundary. Then, we calculate the values of all the relevant parameters by imposing matching conditions. We provide detailed graphical analysis to discuss the physical acceptability of different parameters, namely energy density, pressure, anisotropy and gradient. We also examine the stability of compact stars by exploring energy conditions, equations of state, conditions of causality, redshift functions, mass functions and compactness functions. Finally, we find that the obtained solutions are physically viable and also having good properties for the compact star models. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate and analyze the behavior of charged compact stars in the modified f (R , ϕ , χ) theory of gravity. When solving the field equations, we assume that Krori– Barua space-time describes the geometry of the inner space [K. Krori and J. Barua, A singularity-free solution for a charged fluid sphere in general relativity, J. Phys. A Math. Gen.  8 (1975) 508]. We further analyzed various physical characteristics for our model, including energy density, pressure components, anisotropy parameter, mass function, compactness element, and redshift through their graphical representations. Additionally, we have checked the equilibrium position by taking Tolman–Oppenheimer–Volkoff equation and stability by using Abreu's criterion [H. Abreu, H. Hernandez, and L. Nunez, Sound speeds, cracking and the stability of self-gravitating anisotropic compact objects, Class. Quantum Grav.  24 (2007) 4631] and relativistic adiabatic index. For our study, we choose Hercules XI, Centaurus XIII, EXO 1785-248, LMC XIV stars for analysis. [ABSTRACT FROM AUTHOR]

In this paper, we have provided a new family of solutions to Einstein–Maxwell field equations of charged spherically symmetric anisotropic matter distribution, related to the description of strange stars, in the background of Rastall-Rainbow gravity. We have constructed the field equations along with cosmological constant (Λ) and quintessence dark energy described by the equation of state w q satisfying the range − 1 < w q < − 1 / 3. We have solved the field equations by the proper choice of some relations like radial pressure with energy density and tangential pressures with the energy density and also a useful form of energy density. Next, we have discussed about the smooth connection between the interior spherically symmetric spacetime and the exterior Reissner–Nordstrom-de Sitter spacetime. To demonstrate the physical viability of our considered model, we have discussed a detailed physical analysis of different parameters analytically and graphically. Our whole graphical analysis has been performed for three compact stars like VelaX-1, SAXJ1808.4-3658 and 4U1820-30 in the context of our solutions. With the help of various suitable conditions for stability, we have examined the stability of our model by checking the radial and tangential sound speeds and the adiabatic index values. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to study the physical characteristics and stability of anisotropic compact stars in energy–momentum squared gravity. We use Tolman solution and consider specific models of this theory to study the viable features of SAX J1808.4-3658, 4U 1538-52 and Her X-1 stars. We explore the behavior of energy density, pressure components, anisotropic factor, energy conditions and equation of state parameter in the interior of considered stars. To check the stability of these stars, we examine the behavior of causality conditions, Herrera cracking approach and adiabatic index. It is found that all the required conditions are satisfied for the proposed models, thus the considered stars are viable as well as stable in this modified theory. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to examine the physical features and stability of anisotropic compact stellar objects in energy–momentum squared gravity. For this purpose, we apply Krori–Barua metric solutions and consider three different models of this modified theory to examine the physical characteristics of Her X-1, 4U 1538-52 and SAX J1808.4-3658 compact stars. We analyze the behavior of various physical quantities such as energy density, pressure components, energy conditions, equation of state parameter and anisotropic factor in the interior of these stars. We then use the estimated values of the sound speed and of the adiabatic index to explore the stability of these compact stars. It is found that all the required conditions are satisfied corresponding to all the selected models. We are therefore allowed to conclude that this modified theory provides viable and stable anisotropic compact stars. [ABSTRACT FROM AUTHOR]

This paper studies the influence of charge on a compact stellar structure also regarded as vacuum condensate star in the background of f (ℜ , 2) gravity. This object is considered the alternate of black hole whose structure involves three distinct regions, i.e. interior, exterior and thin-shell. We analyze these domains of a gravastar for a particular model of this modified theory. In the inner region of a gravastar, the considered equation of state defines that energy density is equal to negative pressure which is the cause of repulsive force on the spherical shell. In the intermediate shell, pressure and energy density are equal and contain ultra-relativistic fluid. The inward-directed gravitational pull of thin-shell counterbalances the force exerted by the inner region of a gravastar allowing the formation of a singularity-free object. The Reissner–Nordström metric presents the outer vacuum spherical domain. Moreover, we discuss the impact of the charge on physical attributes of a gravastar such as the equation of state parameter, entropy, proper length and energy. We conclude that singularity-free solutions of charged gravastar are physically consistent in this modified theory. [ABSTRACT FROM AUTHOR]

In this paper, we study complexity of a static spherically symmetric object containing anisotropic fluid in the background of energy–momentum squared gravity (EMSG). We formulate the field equations and describe the energy content of the fluid via Misner–Sharp as well as Tolman mass definitions. In order to compute the complexity factor, the Riemann tensor is orthogonally split to produce structure scalars which incorporate the fundamental properties of the system. The scalar involving anisotropic pressure and inhomogeneous energy density is chosen as the complexity factor. We consider a minimally coupled model to formulate the condition for vanishing complexity which is employed to formulate two solutions. It is concluded that additional matter source terms appearing due to energy–momentum squared gravity increase the complexity of the system. [ABSTRACT FROM AUTHOR]

In this paper, we study the traversable wormhole solutions for a logarithmic corrected f (R) model by considering two different statements of shape b (r) and redshift Φ (r) functions. We calculate the parameters of the model including energy density ρ , tangential pressure P t and radial pressure P r for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots. [ABSTRACT FROM AUTHOR]

This paper deals with the dynamics of charged plane symmetric collapse with dissipative fluid distribution in the framework of energy–momentum squared gravity. For this purpose, we consider non-static plane symmetric spacetime in the inner and static charged Vaidya spacetime in the outer regions of a star. We use Darmois junction conditions to match the interior and exterior geometries and find that masses of both spacetimes are identical if and only if their correspondence charges are same. To investigate the dynamics of the system, we apply Misner–Sharp and Müler–Israel–Stewart approaches to formulate dynamical as well as transport equations, respectively. We then couple these equations to analyze the effect of physical quantities and modified terms on the collapse rate. A relation among Weyl tensor, electromagnetic field and fluid variables, is also developed. Due to the influence of charge, anisotropic pressure and modified terms, the spacetime is not conformally flat. Further, we assume isotropic fluid and ignore the impact of electromagnetic field which yields the conformally flat spacetime and inhomogeneous energy density. We conclude that the collapse rate reduces as compared to general relativity due to the presence of a charge, effective pressure, heat flux and additional terms of this gravity. [ABSTRACT FROM AUTHOR]

In this paper, we have used the reconstructed Dirac–Born–Infeld (DBI)-essence dark energy density to modify the mass accretions of black holes and wormholes. In general, the black hole mass accretion does not depend on the metric or local Einstein geometry. That is why we have used a generalized mechanism by reconstructing the DBI-essence dark energy reconstruction with f (R) gravity. We have used some particular forms of the scale factor to analyze the accretion phenomena. We have shown the effect of cosmic evolution in the proper time variation of black hole mass accretion. Finally, we have studied the validity of energy conditions and analyzed the Type I–IV singularities for our reconstructed model. [ABSTRACT FROM AUTHOR]

This paper investigates the new definition of complexity factor for the case of irrotational spherical relativistic structure in the Rastall theory of gravity (RTG). To do so, we assumed static spherically symmetric metric with anisotropic self-gravitating fluid. We studied Rastall field equations, generalized nonconservation equation, mass function and physical impacts of Rastall parameter α on various material variables by employing certain observational data of compact objects like PSR J1614-2230, 4U1608-52, SAX J 1808.4-3658, 4U1820-30 and Vela X-1. We obtained structure scalars through orthogonal decomposition of the curvature tensor and then utilize these scalars to find the complexity factor of the self-gravitating spherical structure. We examined that the vanishing complexity factor condition is an effective energy density inhomogeneity and an effective anisotropy of pressure which must cancel each other, employed the condition Y T F = 0. Moreover, we also depicted the solutions of interior formation of spherical stellar object regarding to this vanishing complexity condition. Finally, it is found that the complexity of the system enhances due to the presence of nonminimal to curvature matter couple parameter α. It is very fascinating to report here that these outcomes could be recovered back to former solutions about complexity factor in General Relativity (GR) by imposing α = 0. [ABSTRACT FROM AUTHOR]

Considering an energy density of the form ρ = q r r 0 − n (where q is an arbitrary positive constant with dimension of energy density and n > 0), a shape function is obtained by using field equations of braneworld gravity theory in this paper. Under isotropic scenario wormhole solutions are obtained considering six different redshift functions along with the obtained new shape function. For anisotropic case, wormhole solutions are obtained under the consideration of five different shape functions along with the redshift function ϕ = β ln r r 0 , where β is an arbitrary constant. In each case all energy conditions are examined and it is found that for some cases all energy conditions are satisfied in the vicinity of the wormhole throat and for the rest of the cases all energy conditions are satisfied except strong energy condition. [ABSTRACT FROM AUTHOR]

In this paper, evolution of a Friedmann–Robertson–Walker universe is studied in a higher derivative theory of gravity. The relativistic solutions admitting hybrid expansion law of the universe are explored here. Hybrid expansion law is a general form of scale factor from which one can recover both the power-law expansion and exponential expansion as a special case. The hybrid expansion law is interesting as it addresses the early deceleration phase and presents accelerating phase satisfactorily. It is found that an inflationary scenario with hybrid expansion law is permitted in the R 2 gravity fairly well. We consider universe filled with cosmic fluid that describes by an equation of state (EoS) parameter which varies with time. Consequently, we analyze the time variation of energy density parameter, cosmic pressure, equation of state parameter, deceleration parameter and jerk parameter in the cosmological model. The constraints of the model parameters imposed by the cosmological observational data set are determined. The present value of the deceleration parameter (q) , EoS parameter and the epoch at which the transition of decelerated phase to accelerated phase are estimated. In the higher derivative theory, we obtain some new and interesting cosmological solutions relevant for building cosmological models. [ABSTRACT FROM AUTHOR]