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In this paper, the characteristics of a gravastar in f(Q)$f(\mathcal {Q})$ gravity, which is upheld by Krori–Barua (KB) metric are explored. The authors have used KB metric for the interior and shell regions of the gravastar. The field equations are deduced by using KB metric. In the outside regions of the gravastar, two regular black hole metrics are taken. Additionally, the Israel junction condition to calculate the potential difference across the thin shell concerning different types of regular black holes, such as Bardeen and Hayward is applied. The physical properties like proper length, entropy, energy, equation of state, and stability are also discussed.  [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 current study is devoted to exploring the geometrical configuration of a thin‐shell in the background of symmetric teleparallel gravity. For this purpose, the well‐known cut‐and‐paste approach by matching the inner flat and outer newly calculated class of approximated black hole (BH) solutions in symmetric teleparallel gravity are considered, i.e., uncharged, charged, and anti‐de‐Sitter BHs. The dynamical analysis of thin‐shell configuration by adopting the massive and massless scalar field via Klein‐Gordon's equation of motion is discussed. The effective potential and proper time derivative of shell radius for both massive and massless scalar shells are used to discuss the collapse, expansion, and oscillatory behavior. The stable configuration of thin‐shell is observed through the linearized radial perturbation approach with a phantomlike equation of state, i.e., quintessence, dark energy, and phantom energy. It is noted that stable/unstable behavior of thin‐shell is found after the expected position of the event horizon of an exterior manifold. It is concluded that the stability of a thin‐shell is greater for f(Q)$f(\mathbb {Q})$ BH with cosmological constant as compared to the uncharged and charged f(Q)$f(\mathbb {Q})$ BHs. [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]

We show that small homogeneous solutions to the Einstein–Boltzmann-scalar field system exist globally toward the future and tend to the de Sitter solution in a suitable sense. More specifically, we assume that the spacetime is of Bianchi type I–VIII, that the matter is described by Israel particles and that there exists a scalar field with a potential which has a positive lower bound. This represents a generalization of the work [H. Lee and E. Nungesser, Classical Quantum Gravity 35, 025001 (2018)], where a cosmological constant was considered, and a generalization of [H. Lee and J. Lee, J. Math. Phys. 63, 031502 (2022)], where a spatially flat FLRW spacetime was considered. We obtain the global existence and asymptotic behavior of classical solutions to the Einstein–Boltzmann-scalar field system for small initial data. [ABSTRACT FROM AUTHOR]

We consider a consistent with gravity electron based on the overrotating Kerr-Newman (KH) solution and show that the earlier KH electron models proposed by Carter, Israel and López in 1970–1990 should be modified by the Landau-Ginzburg theory, leading to a superconducting electron model consistent with gravity and quantum theory. Truncated by Israel and López, the second sheet of the KN solution is rearranged and represented in a mirror form as a sheet of the positron, so that the modified KN system forms a quantum electron-positron vacuum interacting with gravity. Regularization of the KN black hole solution creates two new important effects leading to a strong gravitational interaction that acts on the Compton scale contrary to the usual Planck scale of Schwarzschild gravity: (A)—gravitational frame-dragging creates two Wilson loops acting at two boundaries of the modified KN solution, and (B)—formation of the flat superconducting core of the regularized KN solution creates a superconducting electron-positron vacuum state. The Landau-Ginzburg model shows that Wilson loops determine phases of two Higgs fields forming superconducting vacuum state of the modified KN solution, quantum vacuum of the electron-positron pairs. The phases of these Higgs fields correspond to two light-like modes of a classical relativistic ring string. We come to the conclusion that the electron models considered by Israel and López are not complete and must be supplemented by a mirror structure that forms a quantum system consistent with QED. [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]

This paper investigates the geometry of a gravitational vacuum star (also known as a gravastar) from the perspective of f (R , T 2) gravity. The gravastar can be treated as a black hole substitute with three domains: (i) the inner domain, (ii) the intrinsic shell, and (iii) the outer domain. We examine these geometries using Kuchowicz ansatz for temporal metric function corresponding to a specific f (R , T 2) model. We compute a nonsingular radial metric potential for both the interior and intermediate domains. The matching of these domains with exterior Schwarzschild vacuum results in boundary conditions that assist in the evaluation of unknown constants. Finally, we examine various attributes of gravastar domains, such as the equation of state parameter, proper length, energy, and surface redshift. We conclude that the gravastar model is a viable alternative to the black hole in the background of this gravity. [ABSTRACT FROM AUTHOR]

In recent days gravastar has been a very lucrative alternative to black holes, as it does not suffer from the singularity problem as well and it is based on sound physical grounds. Modified Symmetric teleparallel equivalent of gravity also has seen quite a few successes in recent years both in cosmology as well as in astrophysical objects like black holes and wormholes. In this paper, we have considered the charged gravastar in f (Q) formulation and have solved it fully analytically and found various physical characteristics like energy density, entropy and EoS for the gravastar. We have used the Israel junction condition to make some phenomenological predictions regarding the potential of the thin shell around the gravastar. We have also studied the deflection of the angle caused by the gravastar. Finally, we conclude by noting how future radio telescopes could detect the gravastar shadow and how can one distinguish it from the black hole event horizon. • We have considered the charged gravastar in f(Q) gravity. • The physical characteristics like energy density, entropy and EoS for the gravastar are derived analytically. • The Israel junction condition is used to make some phenomenological predictions of the thin shell around the gravastar. • We have also studied the deflection of the angle caused by the gravastar. • We conclude by noting how future radio telescopes could detect the gravastar shadow. [ABSTRACT FROM AUTHOR]

We find the phase diagram of solutions of the charged black hole bomb system. In particular, we find the static hairy black holes of Einstein-Maxwell-Scalar theory confined in a Minkowski box. We impose boundary conditions such that the scalar field vanishes at and outside a cavity of constant radius. These hairy black holes are asymptotically flat with a scalar condensate floating above the horizon. We identify four critical scalar charges which mark significant changes in the qualitative features of the phase diagram. When they coexist, hairy black holes always have higher entropy than the Reissner-Nordström black hole with the same quasilocal mass and charge. So hairy black holes are natural candidates for the endpoint of the superradiant/near-horizon instabilities of the black hole bomb system. We also relate hairy black holes to the boson stars of the theory. When it has a zero horizon radius limit, the hairy black hole family terminates on the boson star family. Finally, we find the Israel surface tensor of the box required to confine the scalar condensate and that it can obey suitable energy conditions. [ABSTRACT FROM AUTHOR]

We consider the static charged black hole bomb system, originally designed for a (uncharged) rotating superradiant system by Press and Teukolsky. A charged scalar field confined in a Minkowski cavity with a Maxwell gauge field has a quantized spectrum of normal modes that can fit inside the box. Back-reacting non-linearly these normal modes, we find the hairy solitons, a.k.a boson stars (depending on the chosen U(1) gauge), of the theory. The scalar condensate is totally confined inside the box and, outside it, we have the Reissner-Nordström solution. The Israel junction conditions at the box surface layer determine the stress tensor that the box must have to confine the scalar hair. Some of these horizonless hairy solutions exist for any value of the scalar field charge and not only above the natural critical charges of the theory (namely, the critical charges for the onset of the near-horizon and superradiant instabilities of the Reissner-Nordström black hole). However, the ground state solutions have a non-trivial intricate phase diagram with a main and a secondary family of solitons (some with a Chandrasekhar mass limit but others without) and there are a third and a fourth critical scalar field charges where the soliton spectra changes radically. Most of these intricate properties are not captured by a higher order perturbative analysis of the problem where we simply back-react a normal mode of the system. [ABSTRACT FROM AUTHOR]

Background: Ultraviolet radiation (UVR) is considered a major risk factor for the development of basal cell carcinoma (BCC). Calculating the relative tumor density (RTD) by adjusting the proportion of BCC lesions relative to the skin surface area at a specific site enables comparison of the proportion of tumors at different anatomical sites and better understanding of the association with sun exposure. Objectives: To characterize anatomical distribution of BCC in the Israeli population using RTD score. Methods: A retrospective, cross‐sectional study that includes all histologically confirmed BCC samples obtained from a major national pathological institute, which receives specimens from numerous surgeons throughout Israel, during the first trimester of 2012. Results: A total of 1,712 skin lesions were diagnosed as BCC during the study period. RTD in the head and neck area was the highest over the body (RTD = 6.6). We found that RTD over the upper arms in males was higher than the proportion of skin surface area (RTD = 1.1). A comparison of RTD values in subsites of the head and neck region indicates that men have higher RTD values for the ears, neck, and scalp than women. However, the nose and eyes areas have female predominance. Conclusions: Using RTD scores, our study demonstrates the unique UVR exposure pattern in the Mediterranean climate of Israel and supports the notion that UVR is an important risk factor for the development of BCC lesions. [ABSTRACT FROM AUTHOR]

The aim of this outline is to investigate the consequences of viscous dissipative self-gravitational collapse in non-static spherically symmetric geometry by adopting a Misner–Sharp approach in the context of f(R) metric formalism. In this outline, we propose a viable f(R) model for the physical significance of a self-gravitating system. We determine the junction conditions between interior and exterior space–times. Furthermore, we extend our work for the dissipative dark source case in both forms of heat transformation and free radiation streaming. Finally, the dissipative variables such as heat flux, bulk, and shear viscosity are evaluated in the dynamical equation and then coupled with full causal transport equations in the background of the Israel–Stewart notion. The present analysis discusses the whole study of self-gravitational collapse and recognizes the form of a reduced collapse due to decreasing gravitational mass density, which depends on thermodynamical collapsing variables. [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]

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In this paper, we generate an exact anisotropic gravastar model using gravitational decoupling technique through minimal geometric deformation in the framework of f (ℜ , T 2) gravity. This novel model explains an ultra-compact stellar configuration whose internal region is smoothly matched to the exterior region. The developed stellar model satisfies some of the essential characteristics of a physically acceptable model such as a positive monotonically decreasing profile of energy density from the center to the boundary and monotonically decreasing behavior of the pressure. The anisotropic factor and Schwarzschild spacetime follows physically acceptable behavior. We find that all the energy bounds are satisfied except strong energy condition inside the ultra-compact stellar structure for the coupling constant of this theory, which is compatible with the regularity condition. • We generate an exact anisotropic gravastar model by gravitational decoupling method. • Developed stellar model satisfies essential features of a physically acceptable model. • All the energy bounds are satisfied except strong energy condition inside the ultra-compact stellar structure. [ABSTRACT FROM AUTHOR]

Abstract: The Red Sea is part of a long system of rifts, which formed as a result of African–Arabian continental breakup during the Oligocene–Miocene. Two phases of volcanism are generally accepted, the first occurring 31mya and the second ∼25mya. Sometime between 20 and 14Ma motion along the Dead Sea fault developed and new plate geometry arose to reflect the collision of Arabia with Eurasia. As a result, extension along the northern Red Sea switched from rift-normal (N60°E) to highly oblique and parallel to the newly formed fault. Sea-floor spreading commenced in the southern Red Sea at about 5Ma leading to a change in the way extension is accommodated along its length. In general the Red Sea is divided into three segments with distinct morphologies and geophysical characteristics: southern (between 15°N and 20°N) – active seafloor spreading, central transition zone (20–23.3°N) with discontinuous axial trough and isolated cells of seafloor spreading, northern dominated by an axial depression is currently in the late stages of continental rifting. Magnetic and gravity data support the differences between the southern and northern sections, while new tomographic studies indicate that the central section behaves as a separate entity that does not act as a transfer zone that gradually transmits processes from south to north. Rifting in the southern Red Sea is under the influence of the Afar plume, while in the north, new evidence points to a strong connection with the Dead Sea fault (fault-parallel and perpendicular features indicating motion parallel to the fault). Motion along the fault may be the stronger force acting on the northern Red Sea and hence, it will behave differently than the southern section. The northern section may act as an area, which transfers motion from seafloor spreading (central-southern Red Sea) to strike-slip (Dead Sea fault). [Copyright &y& Elsevier]

Abstract: The Galilee study area, northern Israel, is at present an uplifted, steep continental margin that formed mainly during the Jurassic and has a large positive isostatic anomaly. Since the Jurassic, it was modified by several tectonomagmatic events, which this study attempts to define and classify by updating, reprocessing and reinterpreting gravity, aeromagnetic and geological data. The prominent Rehovot-Carmel N–S positive reduced-to-pole (RTP) magnetic anomaly caused by the Gevim Volcanics, as well as the coexisting Helez-Gaash high Bouguer gravity and the Pleshet low Bouguer gravity, represent the deep (>5km) Permo-Triassic dominant horst and graben structure of Israel. The Jonah Ridge and Beirut high SW–NE RTP magnetic anomalies in the Levant basin delineate the Levant continental edge that is marked by a deeply buried horst covered by a Late Cretaceous volcanic complex. The Asher and Devora Jurassic volcanics appear to be responcible for the Atlit and Galilee negative magnetic anomalies and for significant negative gravity anomalies which became clear after removing gravity effect of the upper (post-Turonian) light density sediments from the observed gravity. The volcanics extend along a SW–NE belt parallel to the strike of the Moho. It is suggested here that the Carmel-Gilboa fault propagated during the Late Cretaceous from the Levant basin across the Galilee area southeastward to form the Azraq-Sirhan graben in Jordan. As such, it forms a right-step, en echelon, dextral strike-slip fault with associated tectonic basins of various shapes. During the Oligocene and before formation of the Dead Sea transform (DST), the reactivation of the Azraq-Sirhan graben was accompanied by tectonic driven rift propagation in the opposite direction, from Azraq-Sirhan to northwest. It dispersed into many faults and terminated ∼10km west of the present DST. During the Miocene it propagated in the same direction and includes internal volcanic activity. The numerous Miocene-Pliocene volcanic centers on the margins of the DST indicate that the preferred pathway for magmas at that time was not within the deep basins of the DST. [Copyright &y& Elsevier]

The Sea of Galilee (Lake Kinneret) occupies the northern part of the 60-km-long Kinnarot-Bet Shean basin. The basin is inferred to be about 7 km deep based on gravity data, partly supported by findings in the Zemah-1 borehole drilled near the lake's southern shore. Seismic reflection data acquired onshore and in the lake lacks the penetration capacity to image such depths, due to the presence of basalt layers and equipment limitations. In this study we analyze data from a seismic survey conducted in the lake in 1997, which we show reveals a pattern that suggests an ancient fluvial plain in the southwest part of the lake and may also point to an old outlet of the Jordan River to the north of the present one. The Pleistocene depositional pattern in the south part of the lake comprises northward-sloping sedimentary prisms, which are attributed to upwelling of the Zemah diapiric structure to the south and the Kursi depression to the northeast. No clear faulting is evident within the Pleistocene section in the south part of the lake between the basin's marginal faults. This conclusion bears important implications for the ongoing tectonic evolution of the basin and for seismic risk. [ABSTRACT FROM AUTHOR]

Thin gravitating defects with conical singularities in higher codimensions and with generalized Israel matching conditions are known to be inconsistent for generic energy-momentum. A way to remove this inconsistency is proposed and realized for an axially symmetric gravitating codimension-two defect in six-dimensional Einstein gravity. By varying with respect to the brane embedding fields, alternative matching conditions are derived, which are generalizations of the Nambu-Goto equations of motion of the defect, consistent with bulk gravity. For a maximally symmetric defect the standard picture is recovered. The four-dimensional perfect fluid cosmology coincides with conventional FRW in the case of radiation, but for dust it has r4/3 instead of r. A four-dimensional black hole solution with the Schwarzschild form with a short-distance r[?]2 correction is presented. [ABSTRACT FROM AUTHOR]

Abstract  This paper considers the quantum collapse of infinitesimally thin dust shells in 2 1 gravity. In 2 1 gravity a shell is no longer a sphere, but a ring of matter. The classical equation of motion of such shells in terms of variables defined on the shell has been considered by Peleg and Steif (Phys Rev D 51:3992, 1995), using the 2 1 version of the original formulation of Israel (Nuovo Cimento B 44:1, 1966), and Cris�stomo and Olea (Phys Rev D 69:104023, 2004), using canonical methods. The minisuperspace quantum problem can be reduced to that of a harmonic oscillator in terms of the curvature radius of the shell, which allows us to use well-known methods to find the motion of coherent wave packets that give the quantum collapse of the shell. Classically, as the radius of the shell falls below a certain point, a horizon forms. In the quantum problem one can define various quantities that give “indications” of horizon formation. Without a proper definition of a “horizon” in quantum gravity, these can be nothing but indications. [ABSTRACT FROM AUTHOR]