Narrow Results

In this paper, we introduced the black brane solution in Rastall theory and in the context of massive gravity. The ratio of shear viscosity to entropy density is calculated for this solution. Our result shows that the KSS bound violates this theory.

In this paper, we introduce the black hole solution in Rastall theory of gravity in the presence of quintessence and the cloud of strings. Our investigations show that this model meets only second-order phase transition in four dimensions. While both the first- and second-order phase transitions are seen in five dimensions. Therefore, according to the AdS/CFT duality, the confinement–deconfinement phase transition only occurs in five dimensions for this model.

In this short review, we discuss the approach of the commutator algebra of covariant derivative to analyze the gravitational theories, starting from the standard Einstein's general theory of relativity (GTR) and focusing on the Rastall theory. After that, we discuss the important role of the torsion in this mathematical framework.

In the appendix of the paper, we analyze the importance of the nascent gravitational wave (GW) astronomy as a tool to discriminate among the GTR and alternative theories of gravity.

The aim of this paper is to study the charged anisotropic strange stars in the Rastall framework. Basic formulation of field equations in this framework is presented in the presence of charged anisotropic source. To obtain the solutions of the Rastall field equations in spherically symmetric Karori and Barua (KB) type space-time, we have considered a linear equation of state of strange matter, using the MIT bag model. The constraints on the Rastall dimensionless parameter $\gamma$ are also discussed to obtain the physically reasonable solution. We explore some physical features of the presented model like energy conditions, stability and hydrostatic equilibrium, which are necessary to check the physical viability of the model. We also sought for the influence of the Rastall dimensionless parameter on the behavior of the physical features of obtained solution. We plot the graphs of matter variables for different chosen values of the parameter $\gamma$ to inspect more details of analytical investigations and predict the numerical values of these variables exhibited in the tabular form. For this analysis, we choose four different arbitrary models of strange stars with compactness $u(=\frac{M}{R})$ 0.25, 0.30, 0.35 and 0.40. We observed that all the necessary physical conditions are satisfied and the presented model is quite reasonable to study the strange stars.

In this paper, we have explored the non-static anisotropic gravitational collapse and expansion solutions in Rastall theory of gravity. The field equations have been formulated for the non-static and inhomogeneous gravitating source. The Misner–Sharp mass function, auxiliary solution and trapped condition have been used to obtained a trapped surface. The auxiliary solutions have been used to obtain the expansion and collapse solutions; these solutions depend on $C(r,t)$ and parameter $\beta$ (which appears due to parametric form of metric components); also the range of parameter $\beta$ has been examined. The expansion scalar $\mathrm{\Theta }$ depends on parameter $\beta$, in the case of expansion $\mathrm{\Theta }>0$ for $\beta >-2$, while for collapse $\mathrm{\Theta }<0$ with $\beta <-2$. Also, the dynamics of the gravitating spherical source has been discussed graphically with the effects of Rastall parameter $\lambda$. For the physically reasonable fluid, the validity of energy conditions has been discussed for expansion and collapse solutions with the various values of $\lambda$.

The aim of this work is to discuss the evolution of compact stars from the view point of a string fluid in Rastall theory using Krori–Barua (KB) metric as interior geometry. The exterior spacetime is considered as Schwarzschild metric while matching of interior and exterior spacetimes lead to coefficients of KB ansatz. The field equations and dynamical variables of the string fluid are explored. We found the values of Rastall parameter $\eta$ for which the dynamical variables satisfy the energy conditions which shows the existence of physical matter. The model is applied to specific physical features including energy conditions, anisotropy, stability, Tolman–Oppenheimer–Volkoff equation, mass function, compactness and redshift of compact stars, in particular, SAX J1808.4-3658, Vela X-12 and Hercules X-1. It is found that the presented model fulfills all the physical requirements and thus, is realistic. We conclude that the string fluid is responsible for the evolution of compact stars in the cosmos.

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

Observational evidence revealed that in the composition of the Universe, the dark energy is in heap proportion which is mainly responsible for the accelerated expansion of the Universe. The astrophysicists hypothesized that every astrophysical object is likely interact with the dark energy Sakti and Sulaksono [Phys. Rev. D 103 (2021) 084042]. Therefore, researchers are intended to study the astrophysical objects with dark energy interaction. In this paper, we proposed a dark energy stars (composed of with dark matter and ordinary matter) model in the Rastall theory of gravity. The Rastall field equations are obtained in the Tolman–Kuchowicz-type metric. To solve the field equations, the arbitrary constants involved in the field equations (due to Tolman–Kuchowicz ansatz) are obtained by matching the interior geometry with the exterior Schwarzschild geometry. The obtained solution is tested physically by computing some analytical results and plotting graphs of different physical parameters like pressure, density for ordinary matter, density for dark matter, mass function, compactness and surface redshift. Stability of the model is also analyzed by different tests like velocity of sound, adiabatic index and TOV equations. The influence of the Rastall parameter on the model has been studied by plotting graphs and computing numerical values of model’s physical parameters for different values of the Rastall parameter. We infer that our propounded model fulfills all the necessary requirements for a physically plausible model.