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The development and stability of acoustic thin-shell wormholes (WHs) within the context of acoustic black holes are examined in this paper. Utilizing linearized radial perturbations, the stability of these WHs is examined. In this study, a variety of equations of state are taken into account, including barotropic, variable Chaplygin, and phantom-like equations of state. According to the findings, the acoustic black hole structure has an unstable configuration for barotropic fluid. However, as the parameter ℰ gets closer to zero, it does not show any stable or unstable configurations at the event horizon position. For higher values of n and ξ , the resulting structure for the phantom-like variable equation of state (EoS) displays stable behavior away from the horizon while presenting unstable configurations close to the event horizon. The possibility of a stable structure rises as n is increased. Additionally, the constructed structure exhibits stable behavior for n = 1 under extreme acoustic black holes, whereas thin-shell topologies demonstrate unstable behavior outside the event horizon for the generalized Chaplygin variable EoS. However, the structure stabilizes for n = 1 at higher values of ξ. The stability of acoustic thin-shell WHs is higher than that of Schwarzschild thin-shell WHs for smaller values of n , indicating that the acoustic black hole parameter greatly influences the stable configurations of thin-shell WHs. [ABSTRACT FROM AUTHOR]

This paper focuses on the examination of stable and unstable geometrical structures of thin-shell wormholes constructed from Henneaux–Martinez–Troncoso–Zanelli black holes through the Visser cut-and-paste approach. We use the Israel thin-shell formalism for evaluating the stress–energy tensor components of the matter distribution near the wormhole throat. Equations of state, specifically the phantom-like and generalized Chaplygin gas model for exotic matter, are used to conduct an extensive investigation into the stability of the thin-shell. The radial perturbation around the equilibrium throat radius is also considered to explore the stable configuration for specific values of physical parameters. Our results show that the stable zones of these thin-shell wormholes increase as the scalar field parameter ℰ approaches −1. This study gives light on the behavior and dynamics of these wormholes throw light on their potential stability and lead the way for additional theoretical physics research. [ABSTRACT FROM AUTHOR]

This paper investigates the evolutionary phases of a collapsing dissipative star cluster in the presence of dark matter. For this purpose, the minimal coupling model of f(R,T) gravity is used as a candidate for exotic matter in star cluster. The collapse equation is derived from generalized dynamical equations which show the total conservation of energy within the cluster. In this context, the approach of Misner and Sharp is applied to study the phenomenon and differentiate between homologous as well as non-homologous gravitational collapse. The generalized dynamical equations are also connected to modified heat transport equations related to heat flux, viscosity and shear, which deals with Israel–Stewart theory (without removing the thermodynamics heat/viscous coupling coefficients). It is found that shear-free and non-dissipative fluid give homologous collapse. The dissipation of collapsing star cluster provides a relation between tidal forces and density inhomogeneity. It is theoretically predicted that the presence of exotic matter controlled the collapsing mechanism. [ABSTRACT FROM AUTHOR]

This paper deals with the study of quasi-spherical gravitational collapse in the framework of f (R , T) theory. We will divide geometry of the star into two distinct portions i.e. interior portion and exterior portion. In the interior portion, we consider quasi-spherical Szekeres line element and in the exterior portion we take Vaidya line element. The interior and exterior portions will be glued by using Israel's junction conditions [W. Israel, Il Nuovo Cimento B (1965–1970) 44, 1 (1966); W. Israel, Phys. Lett. A 24, 184 (1967)]. The field equations will be derived in the context of f (R , T) theory for a particular model. Apparent horizons and their time configuration for various desirable cases will also be discussed. [ABSTRACT FROM AUTHOR]

The paper traces the origin of the Middle East conflict and discusses the gradual evolution of the Israel-Palestine conflict from a historical perspective. The paper discusses the peace negotiations undertaken for the region during different periods and the contribution of the international community in reaching a compromise formula. The paper discusses the emergence and the role of Hamas and how it gained political legitimacy. The paper concludes with the views of Israel and India perspective. [ABSTRACT FROM AUTHOR]

In this paper, we inspect the stable geometry of thin-shell wormholes in the background of static spherically-symmetric AdS black holes solution bounded by dark fluid and Chaplygin-like equation of state p = − ℬ / ρ , where p and ρ denote the pressure and energy density that are related through positive constant ℬ. For this purpose, we consider the two equivalent copies of black holes and connected them at the hypersurface through cut and paste approach. Then, we employ the linearized radial perturbation to discuss the stability of the developed wormhole geometry by assuming variable equations of state. We obtain the maximum stable configuration for massive black holes for both barotropic and Chaplygin variable equations of state while for higher values of n , stable regions decrease. It is found that for every selection of physical parameters of black hole geometry with low intensity of Chaplygin dark fluid, we get the stable configuration of thin-shell wormholes. [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]

This paper explores the role of nonlinear electrodynamics on the stable configuration of thin-shell wormholes formulated from two equivalent geometries of Reissner–Nordström black hole with nonlinear electrodynamics. For this purpose, we use cut and paste approach to eliminate the central singularity and event horizons of the black hole geometry. Then, we explore the stability of the developed model by considering different types of matter distribution located at thin-shell, i.e. barotropic model and variable equations of state (phantomlike variable and Chaplygin variable models). We use linearized radial perturbation to explore the stable characteristics of thin-shell wormholes. It is interesting to mention that Schwarzschild and Reissner–Nordström black holes show the unstable configuration for such type of matter distribution while Reissner–Nordström black hole with nonlinear electrodynamics expresses stable regions. It is found that the presence of nonlinear electrodynamics gives the possibility of a stable structure for barotropic as well as variable models. It is concluded that stable region increases for these models by considering higher negative values of coupling constant α and the real constant n. [ABSTRACT FROM AUTHOR]

This paper studies the complex mechanism of evolving charged self-gravitational (dissipating or non-dissipating) systems using a structure scalar Y T F , resulting from the basic procedure of orthogonal decomposition of the Riemann–Christoffel curvature tensor. The influence of electrical charge on the complexity of the considered system is analyzed in detail. We find several analytical Einstein–Maxwell models fulfilling the quasi-homologous ( Q H ) evolution plus the vanishing complexity factor ( C F ′ ) condition. Few of the presented models fulfill the Darmois constraints and exhibit shells, however, others satisfy the Israel constraints on both the boundary surfaces. Finally, some possible applications of the presented solutions are mentioned, which are important from astrophysical stand points. It is expected that some of the provided evolving Einstein–Maxwell fluid configurations may be utilized as a toy model of general frameworks like supernova explosions. It is found that the Q H implies the vanishing of the C F and gives rise to a unique and simplest configuration (Friedmann–Lemaître–Robertson–Walker model) fulfilling the condition Y T F = 0 and evolving in the Q H regime. [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]

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]

Let G be a finite group and ψ (G) = ∑ g ∈ G o (g) , where o (g) denotes the order of g. The function ψ ′ ′ (G) = ψ (G) / | G | 2 was introduced by Tărnăuceanu. In [M. Tărnăuceanu, Detecting structural properties of finite groups by the sum of element orders, Israel J. Math. (2020), doi:10.1007/s11856-020-2033-9], some lower bounds for ψ ″ (G) are determined such that if ψ ″ (G) is greater than each of them, then G is cyclic, abelian, nilpotent, supersolvable and solvable. Also, an open problem aroused about finite groups G such that ψ ″ (G) is equal to the amount of each lower bound. In this paper, we give an answer to the equality condition which is a partial answer to the open problem posed by Tărnăuceanu. Also, in [M. Baniasad Azad and B. Khosravi, A criterion for p-nilpotency and p-closedness by the sum of element orders, Commun. Algebra (2020), doi:10.1080/00927872.2020.1788571], it is shown that: If ψ ″ (G) > ψ ″ (D 2 p) , where p is a prime number, then G ≅ O p (G) × O p ′ (G) and O p (G) is cyclic. As the next result, we show that if G is not a p -nilpotent group and ψ ″ (G) = ψ ″ (D 2 p) , then G ≅ D 2 p . [ABSTRACT FROM AUTHOR]