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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]

Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein's General Theory of Relativity and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the present sense, by "exotic matter" we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of traversable wormholes (i.e. wormholes that can be safely crossed) within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action, namely the traceless f (R , T) theory of gravitation, with R and T being, respectively, the Ricci scalar and trace of the energy–momentum tensor. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, namely redshift and shape functions. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed. [ABSTRACT FROM AUTHOR]

The detection of an unexpected ∼ 2. 5 M ⊙ component in the gravitational wave event GW190814 has puzzled the community of high-energy astrophysicists, since in the absence of further information it is not clear whether this is the heaviest "neutron star" ever detected or either the lightest black hole known, of a kind absent in the local neighborhood. We show in this work a few possibilities for a model of the former, in the framework of three different quark matter models with and without anisotropy in the interior pressure. As representatives of classes of "exotic" solutions, we show that even though the stellar sequences may reach this ballpark, it is difficult to fulfill simultaneously the constraint of the radius as measured by the NICER team for the pulsar PSR J0030+0451. Thus, and assuming both measurements stand, compact neutron stars cannot be all made of self-bound quark matter, even within anisotropic solutions which boost the maximum mass well above the ∼ 2. 5 M ⊙ figure. We also point out that a very massive compact star will limit the absolute maximum matter density in the present universe to be less than 6 times the nuclear saturation value. [ABSTRACT FROM AUTHOR]

For the accurate understanding of compact astrophysical objects, the Tolmann–Oppenheimer–Volkoff (TOV) equation has proved to be of great use. Nowadays, it has been derived in many alternative gravity theories, yielding the prediction of different macroscopic features for such compact objects. In this work, we apply the TOV equation of the energy–momentum–conserved version of the f (R , T) gravity theory to strange quark stars. The f (R , T) theory, with f (R , T) being a generic function of the Ricci scalar R and trace of the energy–momentum tensor T to replace R in the Einstein–Hilbert gravitational action, has shown to provide a very interesting alternative to the cosmological constant Λ in a cosmological scenario, particularly in the energy–momentum conserved case (a general f (R , T) function does not conserve the energy–momentum tensor). Here, we impose the condition ∇ μ T μ ν = 0 to the astrophysical case, particularly the hydrostatic equilibrium of strange stars. We solve the TOV equation by taking into account linear equations of state to describe matter inside strange stars, such as p = ω ρ and p = ω (ρ − 4 B) , known as the MIT bag model, with p the pressure and ρ the energy density of the star, ω constant and B the bag constant. [ABSTRACT FROM AUTHOR]

The possibility that the vacuum energy density ρ Λ is, indeed, varying in time, has been investigated lately from the running vacuum models perspective. Motivated by such models, in this work, we relate the decaying vacuum energy ρ Λ (t) with a scalar field ϕ. We derive the equations of motion from such a premise and implement the first-order formalism in order to obtain analytical solutions to the cosmological parameters. We show that these are in agreement with recent Planck observational data. We discuss the physical consequences of having ρ Λ (t) related to ϕ. [ABSTRACT FROM AUTHOR]

We investigate the consequences of incepting the Bianchi type I metric in the f (R , T) gravity theory field equations. We particularly derive solutions for a matter-dominated universe. From such a scenario, it is possible to predict a late-time de Sitter universe. Moreover, depending on the numerical fitting function for the scale factor, the universe is predicted to bounce and evade the Big Bang singularity. [ABSTRACT FROM AUTHOR]

The f (R) theories of gravity are the most popular, simple and well-succeeded extension of Einstein's General Relativity. They can account for some observational issues of standard cosmology with no need for evoking the dark sector of the universe. In the present paper, we will investigate LRS Bianchi type-I spacetime in f (R) gravity theory within the phantom energy-dominated era. We show that in this formalism the phantom energy-dominated universe is a transient stage and in the further stage of the universe dynamics, it is dominated, once again, by dark energy. Such an important feature is obtained from the model, rather than imposed to it, and may have a relation to loop quantum cosmology. [ABSTRACT FROM AUTHOR]

Wormholes (WHs) are a solution for General Relativity field equations which characterize a passage or tunnel that connects two different regions of spacetime and is filled by some sort of exotic matter that does not satisfy the energy conditions. On the other hand, it is known that in extended theories of gravity, the extra degrees of freedom once provided may allow the energy conditions to be obeyed and, consequently, the matter content of the WH to be nonexotic. In this work, we obtain, as a novelty in the literature, solutions for charged WHs in the f (R , T) -extended theory of gravity. We show that the presence of charge in these objects may be a possibility to respect some stability conditions for their metric. Also, remarkably, the energy conditions are respected in the present approach. In addition, we argue that our framework can be very useful to study the possibility of evolving (2 + 1) and (3 + 1) -dimensional WH spacetime within the context of nonlinear electrodynamics, which open a new window to probe the physical quantities in a WH-type solution. [ABSTRACT FROM AUTHOR]

Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein's General Relativity theory and according to this theory, they need to be filled by an exotic kind of anisotropic matter. In the present sense, by "exotic matter", we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of wormholes within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, named redshift and shape functions, and yield the wormholes to be filled by a phantom fluid, that is, a fluid with equation of state parameter ω < − 1. In possession of the solutions for the wormhole material content, we also apply the energy conditions to them. The features of those are carefully discussed. [ABSTRACT FROM AUTHOR]

Modified gravity models have been constantly proposed with the purpose of evading some standard gravity shortcomings. Recently proposed by Chamseddine and Mukhanov, the Mimetic Gravity arises as an optimistic alternative. Our purpose in this work is to derive Tolman-Oppenheimer-Volkoff equations and solutions for such a gravity theory. We solve them numerically for quark star and neutron star cases. The results are carefully discussed. [ABSTRACT FROM AUTHOR]

Much effort has been made in trying to solve or at least evade the inconsistencies that emerge from general relativity as the framework for a cosmological model. The extradimensional models rise as superb possibilities in this regard. In this work, I present cosmological solutions for Wesson's space-time-matter theory of gravity. A relation between mass variation at cosmological scales and the expansion velocity of the universe is obtained. Such a relation yields novel features on space-time-matter theory of gravity, which are carefully discussed. [ABSTRACT FROM AUTHOR]