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In this paper, we investigate in this paper the Type IV singular bouncing in the framework of f (R ,) theory of gravity where R and mean the curvature scalar and the Gauss–Bonnet invariant, respectively. Cosmological f (R ,) models constrained by the slow-roll evolution is reconstructed and their explicit forms are provided near the bounce and far away from it. One obtains finally two models whose stability is numerically analyzed in this work. Our results show that the stability of the reconstructed models is very affected by their parameters. The model far from the singularity recovers stability quickly than the model near the singularity. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the accelerated expansion of the Universe in the context of f (Q) modified theory of gravity, where Q is a non-metricity scalar which characterizes the gravitational interaction by using parametrization of the deceleration parameter q = α − β H with f (Q) = ξ + λ Q , where ξ and λ are free parameters constrained by the 57 points of H (z) datasets, 1048 points of Pantheon, 10 points from Baryon Acoustic Oscillations (BAO) datasets and the shift parameters from Planck 2018 of Cosmic Microwave Background (CMB). In the purpose of validating our model, we proceed by the Om diagnostic and the energy conditions. Later we discussed how our model statistically supports Λ CDM using AIC c criterion analysis. [ABSTRACT FROM AUTHOR]

In this paper, we introduce two new shape functions of wormholes in f (R , T) gravity. Both shape functions are satisfied by various geometric conditions. We will also discuss the different energy conditions and geometric behavior corresponding to each shape function in different states. Finally, we investigate the system's stability with a solution corresponding to the two shape functions. [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]

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 present an introduction to cosmic inflation in the framework of Palatini gravity, which provides an intriguing alternative to the conventional metric formulation of gravity. In the latter, only the metric specifies the spacetime geometry, whereas in the former, the metric and the spacetime connection are independent variables—an option that can result in a gravity theory distinct from the metric one. In scenarios where the field(s) responsible for cosmic inflation are non-minimally coupled to gravity or the gravitational sector is extended, assumptions about the underlying gravitational degrees of freedom can have substantial implications for the observational effects of inflation. We examine this explicitly by discussing various compelling scenarios, such as Higgs inflation with a non-minimal coupling to gravity, Higgs inflation with a non-minimal derivative coupling, ℛ 2 inflation, and beyond. We also comment on reheating in these models. Finally, as an application of the general results of Palatini ℛ 2 inflation, we review a model of successful quintessential inflation, where a single scalar field acts initially as the inflaton and then becomes dynamical dark energy, in agreement will all experimental constraints. [ABSTRACT FROM AUTHOR]

To make a comparison of energy conditions in the theory of general relativity and in the modified theories, we have considered f (R) , f (R , T) and f (R , T , Q) theories (where R and T are the Ricci scalar and trace of the energy–momentum tensor, respectively, while Q = T a b R a b ) to test the validity of all the four energy conditions. These energy conditions had been derived to check the viability of cosmological as well as astrophysical models. In this paper, we consider the standard Friedmann–Robertson–Walker spacetime representing the homogeneous and isotropic universe, and investigate the available literature on testing energy conditions as well as calculate these conditions ourselves. In order to provide the comparative results, we test these conditions analytically as well as graphically and present how energy bounds in modified theories depend on the values of the involved parameters and its validity within certain limits. We discuss here, that which of the modified theories comply with certain energy conditions, and hence provide a supporting argument on the existence of modified theories. [ABSTRACT FROM AUTHOR]

The relationship between gauge and gravity amounts to understanding the underlying new geometrical local structures. These structures are new tetrads specially devised for Yang-Mills theories, Abelian and non-Abelian in four-dimensional Lorentzian curved spacetimes. In the present paper, a new tetrad is introduced for the Yang-Mills formulation. These new tetrads establish a link between local groups of gauge transformations and local groups of spacetime transformations that we previously called LB1 and LB2. New theorems are proved regarding isomorphisms between local internal groups and local tensor products of spacetime LB1 and LB2 groups of transformations. These new tetrads define at every point in spacetime two orthogonal planes that we called blades or planes one and two. These are the local planes of covariant diagonalization of the stress-energy tensor. These tetrads are gauge dependent. Tetrad local gauge transformations leave the tetrads inside the local original planes without leaving them. These local tetrad gauge transformations enable the possibility to connect local gauge groups Abelian or non-Abelian with local groups of tetrad transformations. On the local plane one, the Abelian group of gauge transformations was already proved to be isomorphic to the tetrad local group of transformations LB1, for example. LB1 is plus two different kinds of discrete transformations. On the local orthogonal plane two is isomorphic to LB2 which is just . That is, we proved that LB1 is isomorphic to which is a remarkable result since a noncompact group plus two discrete transformations is isomorphic to a compact group. These new tetrads have displayed manifestly and nontrivially the coupling between Yang-Mills fields and gravity. The new tetrads and the stress-energy tensor allow for the introduction of three new local gauge invariant objects. Using these new gauge invariant objects and in addition a new general local duality transformation, a new algorithm for the gauge invariant diagonalization of the Yang-Mills stress-energy tensor is developed as an application. This is a paper about grand Standard Model gauge theories - General Relativity gravity unification and grand group unification in four-dimensional curved Lorentzian spacetimes. [ABSTRACT FROM AUTHOR]

This paper is devoted to observe the physical attributes of static spherically symmetric isotropic compact stellar candidates in the context of Rastall theory of gravity. In order to inspect the structural composition of compact objects, the Heintzmann ansatz is taken into account. The unknown parameters associated with Heintzmann ansatz 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, stellar equation and adiabatic index for several choices of Rastall parameter. It is observed that the stars under consideration manifest stable structures corresponding to Heintzmann ansatz in this framework. Moreover, it is shown that for vanishing Rastall coupling parameter, the standard outcomes of general relativity can be retrieved. [ABSTRACT FROM AUTHOR]

In this paper, our purpose is to investigate the anisotropic stellar structure caused by f (R , ϕ) modified gravity, where R represents the Ricci scalar and ϕ represents the scalar potential. This study emphasizes the impact of static spherically symmetric stellar structures using anisotropic distribution. Furthermore, an anisotropic matter source is employed to explore the stability of star formations. To get the value of unknown parameters of the compact structures, we compare the Schwarzschild metric to external geometry. Moreover, we examine the physical attributes of compact objects by presuming a viable f (R , ϕ) = ϕ (R + α R 2) gravity model. We analyze the graphical behavior of density and pressure, the Tolman–Oppenheimer–Volkov equation, energy conditions, mass function, surface redshift, and adiabatic index. It is recognized that all the obtained results deliver emphatic evidence for the stability of our considered realistic stars. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the bouncing behavior of the universe within the framework of f (R , L m) gravity, using a simple form of f (R , L m) = R 2 + L m γ (where γ is a free model parameter) as previously studied. The model predicts a vanishing Hubble parameter in the early and late times, with the deceleration parameter approaching a specific limit at the bouncing point. The EoS parameter is observed to cross the phantom divide line (ω = − 1) near the bouncing point, indicating a significant transition from a contracting to an expanding phase. The model satisfies the necessary energy conditions for a successful bouncing scenario, with violations indicating exotic matter near the bouncing point. Stability conditions are satisfied for certain values of γ near the bouncing point, but potential instabilities in late-time evolution require further investigation. Finally, we conclude that the f (R , L m) gravity model is promising for understanding the universe's dynamics, especially during events like the bouncing phase. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the Friedmann–Lemaitre–Robertson–Walker cosmological models within the framework of Rastall gravity incorporating particle creation. The modified field equations for Rastall gravity are derived and exact solutions are obtained under various assumptions of the scale factor. The qualitative behavior of our solutions depends on the Rastall coupling parameter ψ = k λ. Following Akarsu et al. [Ö. Akarsu et al., Rastall gravity extension of the standard Λ CDM model: Theoretical features and observational constraints, Eur. Phys. J. C 80 (2020) 1050], we have restricted the Rastall coupling parameter ψ (k = 1) to the range − 0. 0 0 0 1 < ψ < 0. 0 0 0 7 at 68% CL from CMB+BAO data. Further, we have discussed the distinct physical behavior of the derived models in detail. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the flat Friedmann–Robertson–Walker (FRW) space time with domain wall and holographic dark energy in the context of f (Q) theory of gravity. The exact solutions of the field equations are obtained using two different forms of varying deceleration parameters: (i) q = − b (t) − 1 and (ii) q = − l t + m − 1. It is observed that the universe is accelerating and expanding. Furthermore, we have also discussed some physical parameters of the investigated model. [ABSTRACT FROM AUTHOR]

In this paper, we explore the particle creation scenario in the context of f(풢) gravity in flat-FLRW metric. For this purpose, from the perspective of thermodynamics and considering an adiabatic universe, we obtain the modified continuity equation in terms of the dynamic number of particles N. On the other hand, we obtain Friedmann’s equations in f(풢) gravity and then write down the continuity equations of the components of matter and dark energy, taking into account the interaction between them. In what follows, by establishing a correspondence between the particle production scenario and f(풢) gravity, we obtain the cosmological parameters in terms of N. After that, we find cosmological solutions using power-law cosmology and compare them with Hubble parameter data. Finally, we fit the current model with Hubble data and plot the best fit in terms of the redshift parameter. [ABSTRACT FROM AUTHOR]

This paper delivers the characterization of a pseudo B-symmetric spacetimes and we illustrate that a pseudo B-symmetric spacetime admitting Codazzi type of B-tensor represents a perfect fluid spacetime and if this spacetime admits the time-like convergence criterion, then the pseudo B-symmetric spacetime fulfills cosmic strong energy criterion and contains pure matter. Besides, we find in a pseudo B-symmetric spacetime with Codazzi type of B-tensor the electric part of the Weyl tensor vanishes and has Riemann and Weyl compatible vector fields. Furthermore, it is established that the chosen spacetime with Codazzi type of B-tensor is conformally flat and represents a Robertson–Walker spacetime. Also, we calculate the scale factor Ψ(t) for these spacetimes in a spatially flat Robertson–Walker spacetime. Finally, we study the impact of this spacetime under f(R) gravity scenario and deduce several energy conditions by considering a new model f(ℛ) = e(αℛ) −ln(βℛ) in which α and β are positive constants. [ABSTRACT FROM AUTHOR]

In this paper, we have provided a discussion regarding the structural properties of a spherical compact stellar object within the background of f (R , G) modified gravity. We have considered that the interior region of the compact stellar body is filled by a composition of anisotropic dark energy and isotropic normal matter which are assumed to be non-interacting. To relate the two stated fluids, we have considered the dark energy density directly proportional to the matter density. In particular, Krori–Barua (K–B) matric potentials are used to explore the solutions of modified field equations corresponding to f (R , G) = R + β R 2 + G m . Next, we have delivered a detailed 3-dimensional graphical analysis to design physically well-behavior and stability of different parameters like energy density, individual pressure components for both dark energy and normal matter and anisotropy. Also, we have explored the stability and physical acceptability criterion by causality conditions, adiabatic index, TOV equation, and Harrison–Zeldovich–Novikov criteria. Consequently, we have discussed the violation of energy conditions for dark energy and hold the same for the normal matter. Here is an important note we have taken for three compact objects like, SAX JI808.4-3658, PSR J1614-2230, and 4U1820-30, for graphical analysis. Furthermore, we have calculated the predicted values of central density, central pressure, and surface pressure for both dark and normal matter. Finally, we concluded that our proposed dark energy stellar configuration maintains all required stability and physical acceptability criteria. [ABSTRACT FROM AUTHOR]

In this paper, we analyze energy density inhomogeneities for charged fluid configuration in the background of f (T) theory and recognize its prime features as computed in GR. The dynamical equations are composed employing Bianchi identities for the standard, f (T) extra terms, and energy-momentum tensor for the electromagnetic field. We evaluate various mathematical models of dissipative and anisotropic fluid distributions in-plane symmetry under f (T) gravity. To proceed with the investigation, we design the f (T) field equations, kinematical quantities, and mass function. We analyzed dynamical variables and Ellis equations in terms of our considered theory. To examine the associated inhomogeneity factors, specific scenarios are illustrated alongside and without dissipation. Within a non-radiating situation, we analyze dust and isotropic and anisotropic matter in the state of electric charge. We examine the inhomogeneity factor of a dissipative fluid via a charged dust haze. We derive that the electromagnetic field fosters matter inhomogeneity, but additional curvature factors make the entire structure more homogenous as time passes. [ABSTRACT FROM AUTHOR]

In this paper, we employ parametrization techniques within the framework of f (T) gravity to investigate the deceleration parameter (DP), a key quantity characterizing the universe's expansion dynamics. By analyzing the DP, we gain valuable insights into the nature of cosmic constituents and their impact on the universe's evolution. We utilize a combination of observational data, including 31 Cosmic Chronometers (CC) measurements, 1048 Type Ia Supernovae (SNIa), 17 Baryon Acoustic Oscillation (BAO) measurements, Cosmic Microwave Background (CMB), 162 Gamma Ray Bursts (GRB), and 24 observations of compact radio quasars (Q). We employ the Markov chain Monte Carlo (MCMC) sampling technique to estimate the best-fit range of model parameters. Cosmological and cosmographic parameters are investigated, and their implications in the context of cosmology have been discussed. We also analyze the statefinder and Om diagnostic to gain deeper insights into the universe's behavior. Furthermore, we conduct statistical analyses to compare our model with the standard Λ CDM model. Our investigation also includes the study of physical parameters, providing comprehensive insights into the cosmological behavior within the f (T) gravity framework. The results and comparisons presented in this work contribute to a deeper understanding of the universe's dynamics and provide valuable implications for the cosmological model under consideration. [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]

f(R,Lm) gravity provides an alternative explanation for the late-time acceleration of the universe without introducing the concept of dark energy. In this paper, the non-static Bianchi type-III spacetimes have been derived by considering f(R,Lm) = f1(R) + f2(R)H(Lm). The solutions of field equations of f(R,Lm) theory of gravity and Bianchi type-III metric have been obtained for some special cases by taking particular metric components. Noether symmetries have been discussed for the derived spacetimes and it was observed that all of the discussed spacetimes must have at least five Noether symmetries. [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 review a recently offered notion of quasi-static evolution of the axial self-gravitating structures at large scales and the criterium to characterize the corresponding evolutionary aspects under the influence of strong curvature regimes. In doing so, we examine the axial source's dynamic and quasi-static behavior within the parameters of various modified gravity theories. We address the formalism of these notions and their possible implications in studying the dissipative and anisotropic configuration. We initiate by considering higher-order curvature gravity. The Palatini formalism of f (R) gravity is also taken into consideration to analyze the behavior of the kinematical as well as the dynamical variables of the proposed problem. The set of invariant velocities is defined to comprehend the concept of quasi-static approximation that enhances the stability of the system in contrast to the dynamic mode. It is identified that vorticity and distinct versions of the structure scalars Y I , Y II and Y KL play an important role in revealing the significant effects of a fluid's anisotropy. As another example of evolution, we check the influence of Palatini-based factors on the shearing motion of the object. A comparison-based study of the physical nature of distinct curvature factors on the propagation of the axial source is exhibited. This provides the intriguing platform to grasp the notion of quasi-static evolution together with the distinct curvature factors at current time scenario. The importance of slowly evolving axially symmetric regimes will be addressed through the distinct modified gravitational context. Finally, we share a list of queries that, we believe, deserve to be addressed in the near future. [ABSTRACT FROM AUTHOR]

In this paper, we generalize our previous results on spin connection for the linear scalar cosmological perturbation in f (T) theory to a wider class of theories which includes a scalar field Φ non-minimally coupled to torsion, and allows Φ -dependence of the function f. The case of f T T = 0 , with a scalar field non-minimally coupled to torsion, needs a special treatment. In both considered cases we derive self-consistent equations of motion for cosmological perturbation using a solution for non-trivial spin connection. [ABSTRACT FROM AUTHOR]

Recently, presence of gravitational and axial anomalies in Riemann–Cartan (RC) spacetime [Garcia de Andrade, Class. Quantum Gravity 38 (2021)] indicates that topological densities expressed in terms of torsion may be very useful in understanding the physics involved. Pontryagin and Euler density may be presented in terms of torsion in teleparallelism. In this paper, computation of these topological torsional densities in Kerr black holes is given. The geometric quantisation of torsion is also discussed in terms of the teleparallel metric. Actually, the recent work of Del Grosso and Poplawski [arXiv: 2107.06112] showed that the torsion quantization appears when torsion is the generator of momentum quantum mechanical commutator. Moreover, Poplawski et al. showed that use of quantum torsion in quantum electrodynamic (QED) may avoid the divergences in Feynmann integrals, process called, a torsion regularization. Here, we compute the momenta components in terms of teleparallel Kerr black hole torsion generator, like a Casimir tensor. The quantum generator, while not yet related by torsion, is seen to be naturally associated to axial torsion skew-symmetric in the teleparallel geometry. An important fact is that from torsion quantization, torsion chirality appears naturally in the Einstein–Cartan spin-torsion analogy, where now spin-angular momentum of the black hole is connected to torsion. Torsional chiral anomalies are shown to diverge at black hole singularity, and then they cannot be canceled at singularity. [ABSTRACT FROM AUTHOR]

The theory of Hybrid metric-Palatini gravity was proposed by Harko et al. [Metric-Palatini gravity unifying local constraints and late-time cosmic acceleration, Phys. Rev. D 85 (2012) 084016.] in 2012 which could explain both local and cosmological observations. In this paper, this theory has been taken into account to obtain static, spherical, and symmetric charged traversable wormhole solutions. The shape of the wormhole is determined in two different cases with the simplest form of scalar field potential. It is obtained that asymptotically flat wormholes are possible in each case. The energy conditions, namely, null, weak, and strong energy conditions are tested in each case and the results are compared. [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 this paper, the traces of conformal twisted signature operators and noncommutative residue for compact manifolds with boundary are considered, the classic gravity representation for manifolds with boundary associated with conformal twisted signature operators and Kastler–Kalau–Walze-type theorems is explored. [ABSTRACT FROM AUTHOR]

In this paper, we investigate an inflation scenario and dark energy in a scaled gravity, R + β R where β is a dimensionless gravity parameter, with a kinetic term. To reduce the associated moduli space, we implement such a parameter in a specific scalar potential given by V (ϕ) = M 4 (1 − (ϕ μ) β). By computing the relevant cosmological observables including the spectral index n s and the tensor-to-scalar ratio r via the slow-roll analysis, we provide certain inflationary constraints on β from the Planck observational and the recent released BICEP/Keck data. By means of a possible Higgs-inflaton coupling, we discuss dark energy in the proposed scaled gravity within such an inflation model. [ABSTRACT FROM AUTHOR]

We investigate some properties of a black hole in a Horndeski gravity theory mimicking EGB gravity at D → 4. Borrowing ideas from quasitopological gravities provide a matter source of dyonic fields, in which the black hole solution carries two charges, electric and magnetic, in the context of the Einstein–Gauss–Bonnet (EGB) gravity. However, due to several limitations of the EGB gravity in D → 4 , we consider a Horndeski gravity theory which can mimic EGB gravity in D → 4. The essential practice used in this paper is the electromagnetic quasinormal modes process, with the goal of discovering the spectrum of such an electromagnetic perturbation over the black hole spacetime. The Wentzel–Kramer–Brillouin (WKB) approximation is used to achieve the desired results. The study shows that both the charges have similar impacts on the quasinormal modes. [ABSTRACT FROM AUTHOR]

This paper investigates the wormhole solutions in Rastall theory of gravity using the Karmarkar conditions. For this purpose, we choose a shape function (SF) that connects two asymptotically flat regions. We also discuss the wormhole configuration by plotting three-dimensional (3D) analysis of the embedding diagram in Euclidean space. Furthermore, we also observe the detailed graphical representation of energy conditions using the considered SF. The violation of energy conditions, especially null energy conditions (NEC), indicates the existence of exotic matter and wormholes. Hence, it can be concluded that our calculated results in the background of Rastall theory of gravity are viable and stable. The exciting feature of this work is the 3D analysis to discuss the viability of wormhole geometry [ABSTRACT FROM AUTHOR]

Kim and Lee [Phys. Rev. D 63 (2001) 064014] studied charged wormholes and Morris–Thorne wormholes in the presence of scalar field using the concepts of general relativity. In this paper, we have also considered same wormholes affected with electric charge and scalar field and extended their study using the framework of f (R , T) gravity with f (R , T) = R + β R 2 + λ T gravity model, where β and λ are constants. We have examined the possibility for minimization of the amount of exotic matter through energy conditions. Further, we have obtained the deflection angle, an important notion in gravitational lensing, by using strong field limit coefficients which may be helpful in the detection of wormholes. [ABSTRACT FROM AUTHOR]

It is an undeniable fact that the negative energy source is essential for the stability of traversable wormholes. Recently, it has been shown that the Casimir energy which is the only artificial source of negative energy till date, could source the negative energy to the traversable wormholes as well. In this paper, we explore the possibility of non-exotic traversable wormholes in 4-D EGB gravity. We use the Yukawa–Casimir shape function and investigate the various energy conditions. We observe that for appropriate choices of shape function and the parameters, traversable wormholes with normal matter at throat can be found. [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 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]

This paper is focused on the investigation of wormhole solutions in f (Q) gravity, where Q denotes the non-metricity scalar. To obtain these solutions, three specific forms of f (Q) gravity models are considered and the shape function, which is responsible for the shape of the wormhole, has been obtained numerically for each model. Further, the energy conditions are checked and the stability of solutions is obtained by determining the adiabatic sound speed in each case. [ABSTRACT FROM AUTHOR]

In this paper, model of gravitational collapse of anisotropic compact stars in a new theory of f (R) gravity has been developed. The author considers the modified gravity model of f (R) = ξ R 4 to investigate a physically acceptable model of gravitational collapse of anisotropic compact stars. First, the author presents a brief review of the development of field equations of gravitational collapse in f (R) gravity for a particular interior metric for compact stars. Then analytical solutions for various physical quantities of collapsing anisotropic compact stars in ξ R 4 gravity have been developed. By analyzing plots of various physical parameters and conditions, it is shown that the model is physically acceptable for describing the gravitational collapse of anisotropic compact stars in f (R) = ξ R 4 gravity. [ABSTRACT FROM AUTHOR]

The matter–anti-matter asymmetry in the early Universe’s history is explained theoretically by the baryogenesis. It is well known that modified gravity theories are highly effective in explaining the Universe’s current accelerated state. In this paper, we examine the gravitational baryogenesis for f(Q,C) gravity, where Q is the non-metricity scalar and C is the boundary term. To perform the baryogenesis, we assume linear, nonlinear and logarithmic forms of f(Q,C). We evaluate the baryon-to-entropy ratio for our models by assuming the power law form of the scale factor a(t) = a0tδ. We also investigate the generalized baryogenesis for our model by assuming the interaction term ∂μ(Q + C). We constrain the model parameters by comparing with the observational value ηB s = 9.42 × 10−11. Our derived models are physically viable. [ABSTRACT FROM AUTHOR]

In this paper, we propose a specialized parameterization for the Hubble parameter, inspired by Λ CDM cosmology, to investigate the cosmic expansion history of the Universe. This parameterization is employed to analyze the universe's late-time behavior within the context of Q n gravity, where Q represents non-metricity. By using data from 57 Hubble data points, 1048 supernova (SNe) data points, and six Baryon Acoustic Oscillation (BAO) data points, we determine the optimal values for the model parameters. Additionally, we explore three distinct cosmological models based on the parameter n , specifically when it takes on the values of 0. 5 5 , 1. 5 and 2. 0. The results of our analysis indicate that our proposed parameterization, along with the associated models for different values of n , predicts an accelerated cosmic expansion phase. [ABSTRACT FROM AUTHOR]

In this paper, the coupled system nonlinear (2 + 1)-dim Broer–Kaup–Kupershmit (BKK) equation under consideration is based on extension of modified rational expansion method. The various kinds of multiple soliton solutions named anti-kink soliton, traveling wave solutions, periodic solution, dark soliton, kink soliton, bright soliton, anti-kink bright solitons, kink bright solitons for nonlinear BKK system are successfully constructed under symbolic computation Mathematica. The calculated results are very interesting, different and novel which have not been investigated in past literature. The graphical demonstration of constructed solutions show by contour, 2D and 3D shape by using computer software Mathematica. The constructed multiple soliton solutions prove that EMRE approach is very straightforward, efficient, reliable and powerful for the investigation of other nonlinear partial differential equations. The investigated results will be described and play a keen role in the study of nonlinear physical phenomena in the area of physics and engineering. [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]

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]

In this paper, we construct the exact interior solutions for compact stellar objects for perfect fluid distribution in phantom region in the framework of a non-conserved theory, i.e. Rastall gravity (RG). Under these circumstances, we develop the Einstein field equations (EFEs) for spherically symmetric metric using general forms of metric potentials, a (r) = B r α + C r β and b (r) = A r γ , here α , β , γ ≥ 2 and α ≠ β. By matching of interior and exterior regions of the metric, we obtain the values of unknown constants of our considering model which helps to sketch the nature of important physical quantities like density, pressure, energy conditions, and stability. Finally, our obtained results lead us to conclude that our solutions are well behaved and physically viable for the specific choices of model parameters for two different stars (Vela X-1 and 4U1820-30). [ABSTRACT FROM AUTHOR]

This paper formulates two charged interior anisotropic spherical solutions through extended gravitational decoupling scheme in the context of f (G , T) theory, where G and T symbolize the Gauss–Bonnet term and trace of the stress–energy tensor, respectively. The inclusion of an extra sector in the isotropic domain results in the production of anisotropy in the inner geometry. This technique splits the field equations into two independent arrays by deforming the temporal and radial metric coefficients, giving rise to the seed and extra fluid distributions, respectively. The Krori–Barua metric potentials are used to calculate solution of the first set, while some constraints are used to solve the unknowns present in the second array. The resulting anisotropic solution is a combination of both the obtained solutions. We inspect the influence of charge as well as decoupling parameter on the physical variables and anisotropic factor. Finally, the viability and stability of the developed solutions are checked by energy conditions and stability criteria, respectively. We conclude that the first solution is viable as well as stable for the particular range of the decoupling parameter, whereas the second solution is viable but not stable. [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]

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]

Horizonless compact objects with light rings are becoming more popular in recent years for numerous motives. In this paper, the conditions under which the throat of a Morris–Thorne wormhole can act as an effective photon sphere are worked out. A specific example which satisfies all the energy conditions in modified theory of gravity is considered and the formation of relativistic images is studied. We have detected photon spheres for the wormhole modeling due to the effect of strong gravitational lensing. Subsequently, we have found the expression for deflection angle in terms of the angular separation between the image and lens by determining the strong-field limit coefficients. It is found to diverge for the impact parameter corresponding to the photon sphere. We observed that the angle of Einstein ring 0 and relativistic Einstein ring n ≥ 1 are completely distinguishable. Given the configuration of the gravitational lensing and the radii of the Einstein ring and relativistic Einstein rings, we can distinguish between a black hole and a wormhole in principle. The stability of wormholes is examined from the positivity of the shape function and satisfaction of the flare-out condition. [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 study, a homogeneous and anisotropic Bianchi type-I universe model is considered taking the cosmological constant as a variable in the context of f (R, T) gravity. The presented model relies on a unique condition of constant jerk parameter as j = 1, which corresponds to a flat Λ CDM model that leads to a variable deceleration parameter. The exact solution of the field equations is obtained under that condition, and the physical and geometrical features of the model are discussed through the paper. The model has been shown to be successful in explaining recent cosmological observations such as the universe's expansion decelerates in the early universe and accelerates in the late universe, in agreement with their current data. [ABSTRACT FROM AUTHOR]