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In this paper, we examine certain aspects of magnetized spacetime solutions within the Einstein–Maxwell–dilaton theory. Specifically, we discuss the Melvin-like universe and compare it to the equivalent solution in the Einstein–Maxwell case. Additionally, we analyze the equatorial circular motions and corresponding electromagnetic fields within this spacetime. Some distinguished properties compared to the magnetized black hole in Einstein–Maxwell case are found. [ABSTRACT FROM AUTHOR]

In [Phys. Rev. D 107, 104008 (2023)], we reported a novel exact closed-form solution which describes asymptotically flat spacetimes in pure ℛ 2 gravity. The solution is Ricci scalar flat, viz. ℛ ≡ 0 everywhere. Whereas any metric with a null Ricci scalar would trivially satisfy the ℛ 2 vacuo field equation, ℛ (ℛ μ ν − 1 4 g μ ν ℛ) + g μ ν □ ℛ − ∇ μ ∇ ν ℛ = 0 , in this paper, we shall show that our solution satisfies a "stronger" version of the ℛ 2 vacuo field equation, viz. ℛ μ ν − 1 4 g μ ν ℛ + ℛ − 1 (g μ ν □ ℛ − ∇ μ ∇ ν ℛ) = 0 , despite the term ℛ − 1 being singular. Even though ℛ identically vanishes, for our solution, the combinations ℛ − 1 ∇ μ ∇ ν ℛ and ℛ − 1 □ ℛ are free of singularity. This exceptional property sets our solution apart from the set of null-Ricci-scalar metrics and makes it a genuinely nontrivial solution. We further demonstrate that, as a member of a larger class of asymptotically de Sitter metrics, our solution is resilient against perturbations in the scalar curvature at largest distances, making it relevant for physical situations where the background deviates from asymptotic flatness. [ABSTRACT FROM AUTHOR]

General theory of relativity can be equivalently formulated on a flat spacetime associating a torsion-free affine connection of non-vanishing non-metricity scalar Q. In this paper, we present an extension of this, viz., the f (Q) theory of gravity, and explore the early evolution of the universe in the background of anisotropic Bianchi-I model. The f (Q) theory in the current setting through its geometric modification is quite successful in explaining the late time accelerated expansion. Here, we note that it accommodates latest released constraints on the inflationary parameters by Planck's collaboration group with excellent precession, but fails to produce a viable decelerated expansion in the radiation dominated era. [ABSTRACT FROM AUTHOR]

In this paper, we introduce and characterize a pseudo-generalized Ricci-recurrent spacetimes and produce an example to verify the existence of such a spacetime. Then we demonstrate that a conformally flat generalized Ricci-recurrent spacetime with certain condition is a pseudo quasi-Einstein spacetime. Besides, it is proved that a pseudo-generalized Ricci-recurrent generalized Robertson–Walker spacetime represents a perfect fluid spacetime. Lastly, we study the impact of this spacetime under f (ℛ , T 2) and f (ℛ ∗) gravity scenario and deduce several energy conditions. [ABSTRACT FROM AUTHOR]

In this work, using a different theoretical approach, we study a homogeneous and isotropic cosmological spacetime filled with a perfect fluid. Using the framework of Brans–Dicke (BD) and Gauss–Bonnet (GB) theories and including a scalar potential, we obtain the analytical solution of the field equations and find the field functions and the relevant expansion parameter of the spacetime. We assume that the BD and GB media can interact with each other, and hence that there is an energy transfer between these two components. Using this approach, we assume that the BD scalar field is related to intrinsic properties of the GB medium. We introduced a power-law scalar field ϕ (t) = ϕ 0 t p and found the appropriate dynamical functions for the different powers p. We found that the expansion rate of spacetime also behaves as a power-law, and the accelerating expansion is always satisfied for this model. We also analyze the stability for physically acceptable critical points for a given scale factor. [ABSTRACT FROM AUTHOR]

Alcubierre's warp-drive was the first to introduce superluminal travel from different approaches. Instead of creating a shortcut through spacetime via a wormhole, geometrodynamics of simultaneously contracting and expanding spacetime were conjectured. However, both methods require exotic matter that violates energy conditions. In this paper, we employ the concept of braneworld that naturally influences spacetime geometrodynamics. Starting from defining and developing the spacetime metric of the braneworld warp bubble, the expression for energy densities as a function of relevant parameters which contributes to the braneworld approach of superluminal travel by hyperspace-drive was derived. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to obtain physically stable stellar models coupled with anisotropic matter distribution in the context of f (ℛ , T 2) theory. For this, we consider a static spherical geometry and formulate modified field equations containing various unknowns such as matter determinants and metric potentials. We then obtain a unique solution to these equations by employing Durgapal–Fuloria ansatz possessing a constant doublet. We also use matching criteria to calculate the values of these constants by considering the Schwarzschild exterior spacetime. Two different viable models of this modified theory are adopted to analyze the behavior of effective matter variables, anisotropy, energy conditions, compactness and redshift in the interiors of Her X-1, PSR J0348-0432, LMC X-4, SMC X-1, Cen X-3, and SAX J 1808.4-3658 star candidates. We also check the stability of these models by using three different physical tests. It is concluded that our considered stars satisfy all the physical requirements and are stable in this modified gravity for the considered parametric values. [ABSTRACT FROM AUTHOR]

In this paper, a tripartite quantum teleportation scheme in de Sitter vacuum is constructed. Then we investigate the influence of vacuum fluctuation, temperature and two-atom distance on performance of the tripartite quantum teleportation. It is found that fidelity drops fast with temperature and evolution time increasing. While temperature is low relatively, the influence of two-atom distance cannot be negligible, the change of fidelity is different with two-atom separation and time varying. The results may be helpful for dealing with quantum information tasks in curve spacetime and exploring the properties of curve spacetime through quantum information means. [ABSTRACT FROM AUTHOR]

In this paper, we discuss Klein–Gordon (KG) oscillators in the (1 + 2) -dimensional Gürses spacetime and under position-dependent mass (PDM) settings. We observe that the KG Gürses oscillators are introduced as a byproduct of the very nature of the Gürses spacetime structure. We report that the energy levels of such KG Gürses oscillators admit vorticity–energy correlations as well as spacetime-associated degeneracies (STADs). Moreover, we introduce a new set of KG pseudo-Gürses oscillators that admits isospectrality and invariance with the KG Gürses oscillators and inherits the same vorticity–energy correlations as well as STADs. [ABSTRACT FROM AUTHOR]

Considering the condition on conservation of energy–momentum tensor (EMT), we study late time cosmological solutions in the context of f (R , T) = R + α T n gravity (where α and n are constants) in a flat Friedmann–Lemaître–Robertson–Walker (FLRW) spacetime. The present model discusses the case of a barotropic perfect fluid as the matter content of the Universe, along with the case when dissipative effects are taken into account. Briefly, assuming a single perfect fluid, we find that the mentioned model is not capable of presenting an observationally consistent picture of the late time accelerated expansion of the Universe; nevertheless, the model leads to admissible solutions when the bulk viscosity is included. In this regard, a consistent setting is found considering the Eckart, Truncated and Full Israel–Stewart theories which determine the behavior of bulk viscosity. In the presence of bulk viscosity, the behavior of the deceleration parameter (DP) shows that the underlying model can describe an acceptable evolution even if the isotropic pressure of matter content of the Universe is negligible. [ABSTRACT FROM AUTHOR]

First, we illustrate that a conformally flat generalized Ricci recurrent spacetime is a perfect fluid spacetime. As a consequence, we prove that such a spacetime represents a dust matter fluid, stiff matter and dark energy era under certain restrictions on the Ricci scalar. Then we establish that such a spacetime is a Robertson–Walker spacetime. Also, we note that in a conformally flat generalized Ricci recurrent spacetime, the fluid is shear-free, vorticity-free and its flow vector is hypersurface orthogonal. We investigate a conformally flat generalized Ricci recurrent spacetime as a solution of curvature-squared gravity theory. In this study, various energy conditions in terms of the Ricci scalar are examined and state that the Universe is in an accelerating phase and satisfies the weak, null, dominant, and strong energy conditions. [ABSTRACT FROM AUTHOR]

This paper investigates the Noether versus Killing symmetries and their associated conservation laws of Bianchi type-V spacetimes. The study is carried out using the Maple RIFSIMP package, which converts a set of nonlinear differential equations into the reduced involutive form (RIF). This technique generates an RIF tree, where each branch is solved to obtain the explicit forms of Noether symmetries. Separate RIF trees are used to represent each group. We derive a general expression for the Noether symmetry connected to homothety, and then we investigate this Noether symmetry in each separate group. To explore whether dark energy is associated with Bianchi type-V spacetime, we examine the energy density of each spacetime obtained in association with the Ricci scalar. The symmetries of the larger groups, 11- and 17-dimensional, are presented separately in the tables. [ABSTRACT FROM AUTHOR]

This paper examines the structure of a gravitational vacuum star (also known as gravastar) in the background of f (ℜ , 2) theory. This hypothetical object can be treated as a substitute of a black hole, with three regions: (i) the internal region, (ii) the intrinsic shell and (iii) the outer region. We examine these geometries using Finch–Skea metric for the radial metric component along with the particular f (ℜ , 2) model. We determine singularity-free solutions for both the inner as well as thin-shell domains. The smooth matching of the interior region with external Schwarzschild spacetime is obtained through Israel matching constraints. Finally, we study various characteristics of gravastar domains including the equation-of-state parameter, proper length, entropy, energy as well as surface redshift. It is found that the compact gravastar structure is a viable alternate to the black hole in the perspective of this gravity. [ABSTRACT FROM AUTHOR]

In this paper, the different properties of generalized Vaidya spacetime are considered. We define the location of horizons. We show that the apparent horizon can contain the event horizon. The locations of all types of horizons are compared with the ones in the usual Vaidya spacetime. We investigate the time-like geodesics in this spacetime. New corrections to Schwarzschild and Vaidya cases appear and we give conditions when these corrections are not negligible. Also, we consider the conformal Killing vector and transform the metric to conformally static coordinates. We introduce a new constant of motion along null and time-like geodesics, which is generated by a homothetic Killing vector. The conformally static coordinates allow diagonalizing of the generalized Vaidya spacetime. The surface gravity has been calculated for the dust and stiff fluid cases. [ABSTRACT FROM AUTHOR]

Studies of accretion toward black holes are found in the literature where dark energy is chosen to act as the accreting agent. Studies of a dynamical system related to such a phase portrait are also available. In this paper, the central engine is opted to be embedded in a dark energy universe. Footprints of the dark energy equation of state are found in the black hole's metric chosen by us. Using the pseudo Newtonian method, the force complexity due to relativity is replaced with simplified terms. Dynamical system for a viscous accretion is constructed. Each point of this said system is a three-coordinated tuple presenting radial inward speed, sonic speed and specific angular momenta one after the other. A bent curve of center equilibrium is found. Two planes are seen which are, respectively, attractor and repeller. Every case is physically interpreted. For a viscous accretion onto a dark energy embedded black hole, it is followed that the center equilibrium points are forming a closed curve taking the origin on its own plane. Though the orbit of such a center equilibrium curve keeps only a part of it in the space of discussion. [ABSTRACT FROM AUTHOR]

In this paper, we consider a charged relativistic spin-1 oscillator under the influence of an internal magnetic flux in a (2 + 1) -dimensional spacetime induced by a spinning point source. In order to analyze the effects of the internal magnetic flux and spin of the point source on the relativistic dynamics of such a vector field, we seek a non-perturbative solution of the associated spin-1 equation derived as an excited state of Zitterbewegung. By performing an analytical solution of the resulting equation, we determine exact results for the system in question. Accordingly, we analyze the effects of spin of the point source and internal magnetic flux on the relativistic dynamics of the considered test field. We see that the spin of such a field can be altered by the magnetic flux and this means that the considered system may behave as a fermion or boson according to the varying values of the magnetic flux, in principle. We observe that the internal magnetic flux and the spin of the point source impact on the relativistic energy levels and probability density functions. Also, our results indicate that the spin of the point source breaks the symmetry of the energy levels corresponding to particle–antiparticle states. [ABSTRACT FROM AUTHOR]

We discuss bosonization of non-Hermitian invariant fermion models in d = 2 spacetime dimensions within the path-integral approach in which the generating functionals associated to the fermion and boson models can be related. We first discuss the symmetric Thirring-sine-Gordon connection and then extend the treatment to bosonize the Gross–Neveu model. [ABSTRACT FROM AUTHOR]

It has been recently shown that the contribution between the horizons determines the Hawking temperature for a multi-horizon spacetime. In this paper, we apply the Hamiltonian–Jacobi method to compute the Hawking temperature for some multi-horizon spacetimes like Schwarzschild–de Sitter (SdS) spacetime, Reissner–Nordstrom–de Sitter (RNdS) spacetime and rotating BTZ (RBTZ) black hole spacetime and also arrive at the same conclusion. There are two contributions to the tunneling process of radiation. The combination of these two contributions gives the radiation with the Hawking temperature with an effective surface gravity. [ABSTRACT FROM AUTHOR]

Considering the visible and the PeV photons from SN1054 to be emitted at similar times at the source, one estimates the value of a fundamental time constant τ arising in the noncommutative spacetime formulation. [ABSTRACT FROM AUTHOR]

In this paper, we revisit the classical mechanism to produce d -dimensional spacetimes via Kaluza–Klein compactification. We made the assumption that the (d + 1) -dimensional bulk geometry ℳ admits a Homothetic Vector Field (HVF)  H relaxing the existence of a zero i.e. H ≠ 0 holds on ℳ and the homothetic bivector F a b (H) = 0. Under these circumstances, we identify the origin of a positive cosmological constant in the d -dimensional spacetime as the homothetic factor representing a geometrical artifact of late time state of the (d + 1) -dimensional bulk spacetime. [ABSTRACT FROM AUTHOR]

This paper provides a simplified description for simulating the coupling of dark energy with baryonic matter by considering a super-dense pulsar PSRJ1614-2230 as the model star. The starting equation of state for modeling the dark energy is motivated by the MIT Bag model for spherically confined hadrons and the observational evidences of its repulsive nature. Einstein field equations are solved in the stellar interior using the generalized framework of Tolman–Kuchowicz spacetime metric. The solutions are then analyzed for various physical parameters such as metric potential, pressure, density, energy conditions, etc. The physical analysis of multiple parameters indicates stable star formation. The proposed stellar model is free from all singularities and also meets the requisite stability criteria. The numerical results obtained for relativistic adiabatic index indicate that the model star is stiff and stable against radially induced adiabatic perturbations. [ABSTRACT FROM AUTHOR]

With the post-Newtonian approximation, the energy of Schwarzschild spacetime in the Weinberg prescription is obtained. The energy for the first post-Newtonian approximation E (1) = m gives the Newtonian treatment of Schwarzschild spacetime. However, for the second post-Newtonian approximation, the energy is shown that E (1) adds extra terms E (2) which consist of the energy stored in the configuration E config , in the gravitational field E field , and a term of surface integral. These extra terms give post-Newtonian corrections to the Newtonian treatment. [ABSTRACT FROM AUTHOR]

In this paper, the (G ′ / G) -expansion method is used to obtain two certain classes of one-parameter exact solutions to the null-geodesics in Ellis–Bronnikov wormhole spacetime. This method has been developed as an effective technique to construct exact analytical solutions for some kind of nonlinear evolution equations and nonlinear partial derivative equations (PDE). At the first stage of this method, a nonlinear PDE is transformed into nonlinear ordinary derivative equation (ODE) of a polynomial form. Therefore, if we initially have a nonlinear ODE of a polynomial form, say, the geodesic equation, then sometimes its solutions can be obtained following to the procedure of (G ′ / G) -expansion method. Here, this method made it possible to obtain some classes of exact analytical solutions of null-geodesic equations in the metric of Ellis–Bronnikov wormholes. [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]

In this paper, [R. K. Muharlyamov and T. N. Pankratyeva, Eur. Phys. J. Plus 136, 590 (2021)] we have proposed a reconstruction method for the kinetic gravity braiding theory in the framework of the flat Friedman–Robertson–Walker spacetime. Here, we develop this method in the Bianchi I spacetime model for a subclass of the Horndeski theory: G 5 ∼ ϕ , G 2 (X) ≠ 0 , G 3 (X) ≠ 0. The Hubble parameter H (t) and the canonical kinetic term X (t) are set a priori. The choice of the function X (t) determines the anisotropic properties of the Universe. This makes it possible to provide believable anisotropy. The presented method allows for a realistic model of the Universe to simply reconstruct some scalar field theory. Reconstruction example is given for anisotropic model of a post-inflationary transition to the radiation-dominated phase. The model is investigated for the absence ghosts and Laplacian instabilities. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate that Robb-Geroch's definition of a relativistic interval admits a simple and fairly natural generalization leading to a Finsler extension of special relativity. Another justification for such an extension goes back to the works of Lalan and Alway and, finally, was put on a solid basis and systematically investigated by Bogoslovsky under the name "Special-relativistic theory of locally anisotropic spacetime". The isometry group of this spacetime, DISIM b (2) , is a deformation of the Cohen and Glashow's very special relativity symmetry group ISIM(2). Thus, the deformation parameter b can be regarded as an analog of the cosmological constant characterizing the deformation of the Poincaré group into the de Sitter (anti-de Sitter) group. The simplicity and naturalness of Finslerian extension in the context of this paper adds weight to the argument that the possibility of a nonzero value of b should be carefully considered. [ABSTRACT FROM AUTHOR]

Wormholes (WHs) require negative energy, and therefore an exotic matter source. Since Casimir energy is negative, it has been speculated as a good candidate to source those objects a long time ago. However, only very recently, a full solution for D = 4 has been found by [R. Garattini, Eur. Phys. J. C79, 951 (2019), doi:10.1140/epjc/s10052-019-7468-y] thus the Casimir energy can be a source of traversable WHs. Soon later [G. Alencar, V. B. Bezerra and C. R. Muniz, arXiv:2104.13952 [gr-qc]] have shown, that this is not true in D = 3. In this paper, we show that Casimir energy can be a source of the Morris–Thorne WH for all spacetime with D > 3. Finally, we add the cosmological constant and find that for D = 3 Casimir WHs are possible, however, the space must always be AdS. For D > 3 , we show that the cosmological constant invert the signal with increasing throat size. [ABSTRACT FROM AUTHOR]

We show that the meaning of the eigenvalues of a radial equation derived from a power-series method was misunderstood. The roots stemming from the truncation of the power series through a three-term recurrence relation are not the energies of the quantum-mechanical model under study but isolated particular eigenvalues of different models. The supposed dependence of the intensity of the magnetic field on the quantum numbers is just an artifact of the truncation method. [ABSTRACT FROM AUTHOR]

In this paper, we consider the scalar mode of gravity as expressed by a conformal factor of the metric and present a model motivated by the Jordan–Brans–Dicke action. The reduced action provides a Lagrangian density in Minkowski space which exhibits a massive particle and an expanding spacetime through a mechanism which is similar to the Higgs mechanism. [ABSTRACT FROM AUTHOR]

The Hawking–Penrose theorem is not covariant under field redefinitions. Should the invariance under such transformations be a true principle in nature, spacetime singularities become dubious objects. We here review the concept of covariant singularities, that is, singularities that are invariant under both spacetime diffeomorphisms and field redefinitions. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the generalized symmetric, static compact objects under anisotropic fluid in the background of Karmarkar embedding class-1 condition. To find the exact solutions of the modified field equations, we consider the gravitational Lagrangian as a linear function of the Ricci scalar and the trace of the stress–energy tensor, i.e. f (ℛ , ) = ℛ + λ , where λ is a constant. By employing the concept of Karmarkar condition, we calculate a g t t metric component, while for a specific form of g r r , the gravitational potential is chosen. To attain the closed-form solutions of the modified field equations, we match the interior spacetime metric with the exterior Schwarzschild metric at the boundary and using the numerical values of mass and radius of the compact stars like PSR J1903+327, 4U 1820-30, LMC X-4, and EXO 1785-248, we constraint some unknown parameters. We have discussed physical stability of the stellar configuration by adopting the energy bounds, Tolman–Oppenheimer–Volkov (TOV) equation, adiabatic index, central density and pressure as well. It is concluded that our resulting anisotropic solutions did well behave and a reasonable degree of precision with recent observations. [ABSTRACT FROM AUTHOR]

Conventional relativistic electrodynamics is set on flat Minkowski spacetime, where all computable quantities are calculated from the flat metric η μ ν . We can redefine the metric of spacetime from the Dirac algebra. In this paper, we study how an electrodynamic interaction can alter the normal gamma matrix to an effective one and result in a shift in the metric perturbatively. The curvature properties inferred from the curved metric are also investigated. We also study how the spin operator is changed under the interaction that contributes to an effective spin operator and how the spin of an electron will be slightly deviated from 1 / 2. Then we perform canonical quantization of the effective Dirac algebra. Finally, we apply our results to the relativistic hydrogen case and demonstrate how such system curves the spacetime metric. [ABSTRACT FROM AUTHOR]

The 1.5 formalism played a key role in the discovery of supergravity and it has been used to prove the invariance of essentially all supergravity theories under local supersymmetry. It emerged from the gauging of the super Poincaré group to find supergravity. We review both of these developments as well as the auxiliary fields for simple supergravity and its most general coupling to matter using the tensor calculus. [ABSTRACT FROM AUTHOR]

Wormholes are speculative structures linking disparate spacetime points. Their geometry can be obtained by solving Einstein equations with tolerating the violation of null energy conditions (NEC). Recently, many researchers have studied different wormholes according to different criteria, and they achieved remarkable results. In this paper, we investigate a series of exact solutions of the static wormhole with smeared mass source geometry in modified f (R) gravity theories. In fact, we consider the Lorentzian density distribution which is coming from a particle-like source. To be more specific, the modified gravity models we consider here are some power laws. We compute resulting solutions according to the wormhole field equations. We also specify parameters such as the radial pressure and transverse pressure as well as various energy conditions such as NEC, weak energy conditions and strong energy conditions. Finally, by plotting some figures, in addition to identifying the wormhole throat, we describe the results of either the violation or the satisfaction of the energy conditions completely. [ABSTRACT FROM AUTHOR]

In this note, we revise the problem of the axial anomaly in the framework of Very Special Relativity following Fujikawa's path integral approach. We show nonperturbatively that no VSR contribution is present in the path integral measure in (3 + 1)-dimensional spacetime. Furthermore, we extend our results to (1 + 1) dimensions, as well as to the two-dimensional curved spacetime. [ABSTRACT FROM AUTHOR]

In this paper, we use the idea of modified Newtonian dynamics to further support the arguments that important information concerning the nature of space is hidden at hadronic mass and distance scales. [ABSTRACT FROM AUTHOR]

As a fundamental cryptographic primitive, bit commitment has lots of important and practical applications in modern cryptography. All previously proposed non-relativistic quantum bit commitment protocols cannot evade the Lo–Chau and Mayers attacks. Furthermore, relativistic quantum bit commitment protocols require rigorous spacetime constraints. In this paper, we present a simple, feasible but practically secure quantum bit commitment protocol without any spacetime constraint. The security of the proposed protocol is based on non-relativistic quantum mechanics, but it can resist all known attacks, including the Lo–Chau and Mayers attacks in practice. [ABSTRACT FROM AUTHOR]

We investigate the existence and stability of both the timelike and null circular orbits for a (2 + 1)-dimensional charged BTZ black hole in Einstein-nonlinear Maxwell gravity with a negative cosmological constant. The stability analysis of orbits is performed to study the possibility of chaos in geodesic motion for a special case of black hole so-called conformally invariant Maxwell spacetime. The computations of both proper time Lyapunov exponent (λ p) and coordinate time Lyapunov exponent (λ c) are useful to determine the stability of these circular orbits. We observe the behavior of the ratio (λ p / λ c) as a function of radius of circular orbits for the timelike case in view of different values of charge parameter. However, for the null case, we calculate only the coordinate time Lyapunov exponent (λ c) as there is no proper time for massless test particles. More specifically, we further analyze the behavior of the ratio of λ Null to angular frequency (Ω c) , so-called instability exponent as a function of charge (q) and parameter related to cosmological constant (l) for the particular values of other parameters. [ABSTRACT FROM AUTHOR]

Starting from a regular, static and spherically symmetric spacetime, we present a stellar model formed by two sources of ordinary and quintessence matter both with anisotropic pressures. The ordinary matter, with density ρ , is formed by a fluid with a state equation type Chaplygin P r (ρ) = μ c 2 ρ − ν / (c 2 ρ) for the radial pressure. And the quintessence matter, with density ρ q , has a state equation P r (ρ q) = − c 2 ρ q for the radial pressure and P r (ρ q) = − (1 + 3 w) c 2 ρ q / 2 for the tangential pressure with − 1 < w < − 1 3 . The model satisfies the required conditions to be physically acceptable and additionally the solution is potentially stable, i.e. v t 2 − v r 2 < 0 according to the cracking concept, and it also satisfies the Harrison–Zeldovich–Novikov criteria. We describe in a graphic manner the behavior of the solution for the case in which the mass is 1. 3 M ⊙ and radius R = 8. 8 4 9 km which matches the star EXO 1785-248, from where we obtain the maximum density ρ c = 1. 2 0 6 5   1 0 1 8 kg / m 3 for the values of the parameters μ = 0. 1 5 5 3 5 , w = − 0. 3 3 3 3 4. [ABSTRACT FROM AUTHOR]

Usual uniformly accelerated frame, in Dray–'t Hooft spacetime, does not see the any quantum imprint on Unruh effect due to localized shock wave in Minkowski spacetime. Here, we argue that such non-appearance of quantum memory is specific to those particular observers which do not incorporate the presence of wave in their trajectory. In fact, a detector, associated with a frame which is affected by the shock, cannot be trivial in terms of its response. We explicitly show that the later type of frame detects particle in the shock wave Minkowski vacuum which is the effect of shock. Therefore, this quantum memory is very special to specific class of observers as far as Dray–'t Hooft spacetime is concerned. We analyze for a null like trajectory along which the detector is moving. [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]

The precession effect of periastron for a massive test particle in the spacetime of a Janis–Newman–Winicour wormhole is studied in the weak field limit. Based on the metric of this static and spherically symmetric wormhole in harmonic coordinates, we derive the second post-Newtonian dynamics of the particle. The second-order orbital precession of periastron is then obtained via a post-Newtonian iterative technique under the Wagoner–Will–Epstein–Haugan representation. Our result is found to be consistent with the classical precession effect when the asymptotic scalar charge is dropped. [ABSTRACT FROM AUTHOR]

In this work, we analyze the motion properties of the test particle, that has a variable mass within the frame of Hénon–Heiles system. We derive the equations of motion of the test particle which varies its mass according to Jean's law. We also determine the quasi-Jacobi integral which shows the effective variation due to variable mass parameters. Further, we studied the locations of stationary points and their stability, after using Meshcherskii spacetime inverse transformations. [ABSTRACT FROM AUTHOR]

The simultaneity framework describes the relativistic interaction of time with space. The two major proposed simultaneity frameworks are differential simultaneity, in which time is offset with distance in "moving" or rotating frames for each "stationary" observer, and absolute simultaneity, in which time is not offset with distance. We use the Mansouri and Sexl test theory to analyze the simultaneity framework in rotating frames in the absence of spacetime curvature. The Mansouri and Sexl test theory has four parameters. Three parameters describe relativistic effects. The fourth parameter, 𝜖(v), was described as a convention on clock synchronization. We show that 𝜖(v) is not a convention, but is instead a descriptor of the simultaneity framework whose value can be determined from the extent of anisotropy in the unidirectional one-way speed of light. In rotating frames, one-way light speed anisotropy is described by the Sagnac effect equation. We show that four published Sagnac equations form a relativistic series based on relativistic kinematics and simultaneity framework. Only the conventional Sagnac effect equation, and its associated isotropic two-way speed of light, is found to match high-resolution optical data. Using the conventional Sagnac effect equation, we show that 𝜖(v) has a null value in rotating frames, which implies absolute simultaneity. Introducing the empirical Mansouri and Sexl parameter values into the test theory equations generates the rotational form of the absolute Lorentz transformation, implying that this transformation accurately describes rotational relativistic effects. [ABSTRACT FROM AUTHOR]

For the first time, we present Einstein's cluster model in embedding class one spacetime. This paper shows that for any neutral configurations there is only one Einstein cluster solution in embedding class one. In fact, one can find two solutions where the first solution i.e. g r r = e λ = 1 and g t t = e ν = C is an unphysical one as it has zero density profile as well as violates the Pandey–Sharma condition (i.e. not a class one solution). However, the second solution can describe matter distribution representing Einstein's cluster which is in static and equilibrium as it satisfies the static stability criterion and TOV-equation. The second solution not only satisfies the above conditions, but also satisfies the energy conditions. The equation of state parameter ω t is less than unity signifying that it can represent physical matters. Further, we have also shown that the Einstein's clusters may also exhibit the properties of compact stars. [ABSTRACT FROM AUTHOR]

For the first time, we choose non-flat vacuum mode for background spacetime based on the minimum number of created particles during early non-de Sitter inflation. In conventional methods for calculating the number of created particles, the flat background is selected automatically and causes a negative number problem for created particles during asymptotic-de Sitter inflation. In a covariant approach to curved spacetime, both real and background spacetimes should be selected, curved and consequently the relation for particle creation should be modify. As an interesting finding from this research, flat space does not include minimum number of particles and there are some asymptotic de Sitter spacetimes with fewer number. Therefore, in the generalized formula for particle creation, we choose a non-flat background containing the minimum number of created particles. [ABSTRACT FROM AUTHOR]

We investigate the generalized form of Duffin–Kemmer–Petiau (DKP) equation in the presence of both a position-dependent electrical field and curved spacetime for the 2-dimensional anti-de Sitter spacetime. Moreover, we derive both the asymptotic wave function and construct energy quantization with the help of the properties of gamma function. All thermodynamic quantities of the system have been calculated with the help of the Euler–MacLaurin formula in the final state. [ABSTRACT FROM AUTHOR]

In this paper, we show that the causally connected four-dimensional line element of the κ -deformed Minkowski spacetime induces an upper cut-off on the proper acceleration and derive this maximal acceleration, valid up to first order in the deformation parameter. We find a contribution to maximal acceleration which is independent of ℏ and thus signals effect of the non-commutativity alone. We also construct the κ -deformed geodesic equation and obtain its κ -deformed Newtonian limit, valid up to first order in deformation parameter. Using this, we constrain non-commutative parameters present in the expression for maximal acceleration. We analyze different limits of the maximal acceleration and also discuss its implication to maximal temperature. We also obtain a bound on the deformation parameter. [ABSTRACT FROM AUTHOR]

We argue in a quantitative way that the unitarity principle of quantum field theory together with the quantum information bound on correlation functions is in tension with a space which is made out of disconnected patches at microscopic scales. [ABSTRACT FROM AUTHOR]

The generalized Duffin–Kemmer–Petiau (DKP) oscillator with electromagnetic interactions in the curved spacetimes is investigated. We introduce firstly the generalized DKP oscillator in Som–Raychaudhuri spacetime with Cornell potential. Then, we consider the electromagnetic interactions into the generalized DKP oscillator. The energy eigenvalues and eigenfunction of our problem are obtained. The effects from the parameters of spacetime, the frequency of oscillator, the Cornell potential and the magnetic flux on the energy eigenvalues have been analyzed. We find an analog effect for the bound states from the Aharonov–Bohm effect in our considered system. [ABSTRACT FROM AUTHOR]