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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]

This paper examines the structure of gravastar (gravitationally vacuum star) in the background of f (ℜ , 2) theory. The gravastar can be regarded as a substitute for a black hole comprising of three regions (i) the interior domain, (ii) the intrinsic shell and (iii) the exterior domain. We investigate these domains by employing Karmarkar's condition by assuming a specific f (ℜ , 2) model. The field equations are solved to evaluate nonsingular solutions of both the interior and intermediate regions. Inner as well as outer spacetimes are matched together using Israel formalism to obtain density and pressure at the joining surface. Different attributes of gravastar like the equation of state parameter, proper length, entropy and energy are analyzed through graphical behavior. It is found that the gravastar model is a viable alternative to the black hole in the context of this gravity. [ABSTRACT FROM AUTHOR]

The cosmological model executing hybrid expansion law (HEL) of scale factor in Randall–Sundrum type II (RS) braneworld gravity with Gauss–Bonnet terms in the presence of bulk viscosity described by Eckart theory, Truncated Israel–Stewart (TIS) theory, Full Israel–Stewart (FIS) theory and nonlinear Israel–Stewart (nIS) theory is studied. In the hybrid expansion law, the scale factor of the universe is described by the product of power-law and exponential expansions. In the HEL model, the early inflation and its transition from deceleration phase to present accelerated phase of expansion can be explored. The constraints of hybrid expansion law model parameters are determined using the recent observational data. Thereafter, the estimated parameters are considered to explore the present value of deceleration parameter, jerk parameter and transition epoch from early deceleration to the present accelerating phase. [ABSTRACT FROM AUTHOR]

This paper is devoted to studying the structure of gravitationally vacuum condensate stars under the influence of matter and geometry coupled gravity. This alternative to black hole comprises three domains, i.e. interior, exterior and thin-shell. We investigate such regions by considering particular equations of state for a specific model of energy–momentum squared gravity. The nonsingular solutions of field equations are obtained to describe the interior region of gravastar and the Schwarzschild spacetime represents the exterior region. The junction conditions are used to match interior and exterior domains while Lanczos equations provide the surface density and pressure at thin-shell. We investigate various attributes of gravastar such as the equation of state parameter, entropy, proper length as well as energy. The physical features of a gravitationally vacuum star indicate a linear relationship with the thickness of the shell and provide a viable structure similar to general relativity. [ABSTRACT FROM AUTHOR]

The Israel junction conditions of a thin shell in the context of Einstein–Cartan gravity are revisited. It is shown that with a choice of the torsion discontinuity taken to be orthogonal to the hypersurface and consistent with the antisymmetric properties of torsion tensor and contorsion tensor, the generalized asymmetric surface energy–momentum tensor turns out to be tangent to the hypersurface while the resulting generalized Israel junction conditions are modified. The main differences to previous works are mentioned. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the effects of shear viscosity on a dissipative spherical collapse in the presence of heat dissipation and anisotropic pressure. In the background of f (R , T , Q) gravity, where R is Ricci scalar, T constitutes the trace of energy–momentum tensor, and Q ≡ R μ ν T μ ν , we examine the particular role of shear viscosity on the dynamical equations, and couple it with the heat transport equation, which is interpreted by Israel–Stewart theory. We reacquire the reduction in the inertial mass density of the matter with the addition of viscosity terms, by a factor (1 − α) which depends upon the inner states of thermodynamics. With the conformity of the equivalence relationship, the decline in inertial density is very close to gravitational force. To determine the particular results, we construct a relationship of Weyl tensor with distinctive matter variables. We study the inhomogeneous characteristics of energy density in this scenario and examine the significant effects of modified gravity along with shear viscosity. [ABSTRACT FROM AUTHOR]

The illustration of cosmic acceleration is being presented in the framework of DGP braneworld and dynamical Chern–Simons modified gravity in the presence of casual Israel–Stewart formalism. In this way, we discuss the evolution parameter which leads to the accelerated expansion of the universe in the phantom as well as quintessence region for both gravities. The squared speed of sound ( v s 2) leads to the stable behavior of the current physical system in both gravities in the later epoch. Also, the entropy variation, as well as thermal equilibrium condition, remains valid in both frameworks at the present and later epoch. [ABSTRACT FROM AUTHOR]