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In the region where the gravitational field is strong, we have examined the influence of different gravities on the accretion disk formed due to spherical accretion. To achieve this, we obtain numerical solutions of the GRH equations, utilizing Schwarzschild, Kerr, Einstein–Gauss–Bonnet, and Hartle–Thorne spacetime metrics. We investigate the impact of the rotation parameter of a black hole (a ∕ M), the EGB coupling constant (α), and the quadrupole moment of the rotating black hole (q) on the accretion disk formed in a strong field. The formation of the disk for the slowly and rapidly rotating black hole models is separately examined, and comparisons are made. Our numerical simulations reveal that, under the specific conditions, the solution derived from Hartle–Thorne gravity converges toward solutions obtained from Kerr and other gravitational models. In the context of the slowly rotating black hole with a ∕ M = 0. 2 8 , we observe a favorable agreement between the Hartle–Thorne result and the Kerr result within the range of 0 < q < 0. 5. Conversely, in the scenario of the rapidly rotating black hole, a more pronounced alignment with the value of q = 1 is evident within the range of 0. 5 < q < 1. Nevertheless, for q > 1 , it becomes apparent that the Hartle–Thorne solution diverges from solutions provided by all gravitational models. Our motivation here is to utilize the Hartle–Thorne spacetime metric for the first time in the numerical solutions of the GRH equations for the black holes, compare the results with those obtained using other gravities, and identify under which conditions the Hartle–Thorne solution is compatible with known black hole spacetime metric solutions. This may allow us to provide an alternative perspective in explaining observed X-ray data. [ABSTRACT FROM AUTHOR]

Combining quantum theory with the fundamental principles of gravity results in the modification of the uncertainty principle. In this study, we employ the extended uncertainty principle (EUP) with the maximum length derived from the cosmological particle horizon. The impact of this specific kind of modification is examined in a non-interacting electron gas system. We analytically derive the generalized relations for the degeneracy pressure and the bulk modulus. An intriguing finding is that the degeneracy pressure is reduced, as confirmed by the observed size of white dwarfs, which is smaller than what is predicted by the standard theory. Nevertheless, it is still capable of providing support against gravitational collapse. [ABSTRACT FROM AUTHOR]

We consider the problem of gravitational collapse of a fluid under the effect of a small Schwarzschild black hole (e.g. a primordial one). We assume the fluid initially may be approximated by a uniform homogeneous dust. Starting from this configuration we obtain a class of metrics under some physically justified assumptions. We find that the metric we obtain includes the dust collapse as a subcase. After discussing some basic properties of the solution, we discuss the case of dust collapse in more detail. We find that the radial and tangential pressures outside the horizon may take positive or negative values depending on the values of the parameters. [ABSTRACT FROM AUTHOR]

This work analyzes the dynamical variables and information transfer of a collapsing string fluid in the theory of Rainbow gravity (RG). Modifications are made to the field equations for the anisotropic string fluid in spherical geometry with the necessary rainbow functions. We have calculated the radius and time when effective horizons formed. This calculation helps to estimate the time of the observer reaching the apparent horizon. Moreover, we have computed the dynamical variables concerning the string fluid including mass density, pressure and the string tension. The behavior of the dynamical quantities is presented graphically. It is found that the rainbow parameter η affects the dynamical variables. The results enable us to understand the physics of a collapsing fluid and the information transfer in the collapsing scenario. [ABSTRACT FROM AUTHOR]

In this paper, we adapted the Appleby–Battye–Starobinsky model of F (R) gravity towards describing double cosmological inflation and formation of primordial black holes with masses up to 1 0 1 9  g in the single-field model. We found that it is possible to get an enhancement of the power spectrum of scalar curvature perturbations to the level beyond the Hawking (black hole evaporation) limit of 1 0 1 5  g, so that the primordial black holes resulting from gravitational collapse of those large primordial perturbations can survive in the present universe and form part of cold dark matter. Our results agree with the current measurements of cosmic microwave background radiation within 3 σ but require fine-tuning of the parameters. [ABSTRACT FROM AUTHOR]

In this paper, the higher-dimensional collapse of homogeneous isotropic perfect fluid is studied by considering the geometry of five-dimensional spherically symmetric metric. Using equations of state for different fields like dust, radiation and stiff fluid with and without cosmological constant Λ , the gravitational collapse is studied. The results are compared with the usual four-dimensional study in [A. V. Astashenok, K. Mosani, S. D. Odintsov and G. C. Samanta, Int. J. Geom. Methods Mod. Phys. 16, 1950035 (2019)]. It is found that the collapse rate is faster in five-dimensional spacetime as compared to four-dimensional case supporting the cosmic censorship hypothesis. [ABSTRACT FROM AUTHOR]

In this review of Low Energy Nuclear Astrophysics, we review the nuclear energy and evolution of the sun. Then we review the estimate of dark matter from galaxy rotation. Next, we discuss neutron star formation from the gravitational collapse of massive stars which produces neutron stars and their velocity. Then the origin of supernovae, the estimate of dark energy from supernovae acceleration, and experiments related to low energy nuclear astrophysics are reviewed. [ABSTRACT FROM AUTHOR]

Dynamics of charged rotating BTZ black holes in 2 + 1 dimensions by using the cut and paste approach is discussed. Due to the mechanical stability of rotating charged BTZ thin shell, the radial perturbation about the equilibrium throat radius and three variable equation of state (EoS) is analyzed. Several examples are displayed satisfying it, such as variable Phantom-like, variable Chaplygin gas and variable modified generalized Chaplygin gas. [ABSTRACT FROM AUTHOR]

In this paper, the spherically symmetric gravitational collapse of anisotropic fluid in the presence of charge in metric f (R) theory is analyzed. We consider the static and non static spherically symmetric spacetimes for outer and inner regions of collapsing object respectively. For the smooth matching of inner and outer regions, the Senovilla as well as Darmois matching conditions are utilized. The closed form solutions are obtained from field equations. Moreover, we examine the apparent horizons and their physical significance. The effect of cosmological constant and f (R) term is same and the collapsing rate speeds up as compared to that of anisotropic fluid case when the electromagnetic field is introduced. Electromagnetic charge also affects the time interval of singularities and cosmological horizons. [ABSTRACT FROM AUTHOR]

In this paper, we employ the Karmarkar condition to model a spherically symmetric radiating star undergoing dissipative gravitational collapse within the framework of classical general relativity. The collapse ensues from an initial static core satisfying the Karmarkar condition in isotropic coordinates and proceeds nonadiabatically by emitting energy in the form of a radial heat flux to the exterior Vaidya spacetime. We show that the dynamical nature of the collapse is sensitive to the initial static configuration that inherently links the embedding to the final remnant. Our model considered several physical tests on how an initially static stellar structure onset to a radiative collapse. [ABSTRACT FROM AUTHOR]

This paper is devoted to analyzing the stability of charged anisotropic cylinder using the radial perturbation scheme. For this purpose, we consider the non-static cylindrically symmetric self-gravitating system and apply both Eulerian as well as Lagrangian approaches to establish a linearized perturbed form of dynamical equations. The conservation of baryon number is used to evaluate perturbed radial pressure in terms of an adiabatic index. A variational principle is developed to find a characteristic frequency which helps to examine the combined effect of charge and anisotropy on the stability of gaseous star. It is found that dynamical instability can be prevented until the radius of cylinder exceeds the limit R ≥ 1 8 and anisotropy increases the instability up to the limiting value of β = − 1. 5. Finally, we conclude that the system becomes more stable by increasing the definite amount of charge gradually. [ABSTRACT FROM AUTHOR]

In this paper, we have used the Karmarkar condition to the spherically symmetric non-static radiating star experiencing dissipative gravitational collapse with a heat flux in the framework of f (R , T) gravity, (where R is Ricci scalar which replaces Lagrangian density and T is the trace of energy–momentum tensor). To obtain the ultimate results of the gravitational field equations in f (R , T) scenario, we take a linear form of the function as f (R , T) = R + 2 λ T. In this connection, the Karmarkar condition along with boundary condition generates a model of radiating star and enables us to completely indicate the spatial presence of gravitational potentials. Vadiya's exterior solution across a time-like hypersurface is smoothly matched to the interior solution which allows to study the physical conduct of our model under consideration. Furthermore, we have analyzed the energy conditions of radiating star in f (R , T) gravity and analyzed the physical behavior of thermodynamics parameters which provide a detailed discussion of the model. For coupling parameter λ = 0 , we successfully obtain the standard results of General Relativity. [ABSTRACT FROM AUTHOR]

Gravitational collapse of a spherically symmetric homogeneous perfect barotropic fluid with linear as well as polytropic-type Equation of State (EoS) has been investigated in the framework of a linear model of f (R , T) gravity. This modified gravity has the potential to explain the observed cosmic acceleration. The calculations have been done taking the transformed time coordinate t → ρ 0 3 t , where ρ 0 is the initial density of the fluid. For linear EoS p = ω ρ , the condition for being a true singularity, along with sufficient condition for the formation of apparent horizon covering the singularity has been derived. For a polytrope having the EoS p = K ρ 1 + 1 n , the scale factor (A) as a function of fluid density (ρ) has been obtained which is then used to study the dynamics of the fluid. Role of the polytropic index (n) and the constant of proportionality (K) in the dynamics of the fluid is also studied. A new type of exotic matter field having varied dependence of scale factor on the density, and having the potential to give rise to bouncing cosmology, provided it is the dominating fluid in the universe, is obtained in this domain and is investigated. Energy conditions are discussed. [ABSTRACT FROM AUTHOR]

In this paper, we consider a non-static cylindrically symmetric self-gravitating system with anisotropic matter configuration and investigate its stability regions by using a homogenous model. We establish perturbed form of dynamical equations by using Eulerian and Lagrangian approaches. The conservation of baryon number is applied to obtain adiabatic index as well as perturbed pressure. A variational principle is used to find characteristic frequency which helps to compute the instability criteria. It is found that dynamical instability can be prevented till the radius of a cylinder exceeds the limit R > 18. We conclude that the system becomes unstable against radial oscillations as the radial pressure increases relative to tangential pressure. [ABSTRACT FROM AUTHOR]

This paper studies the dynamics of thin-shell for (2 + 1)-dimensional rotating and charged rotating Bañados–Teitelboim–Zanelli black holes by using Israel thin-shell formalism. We consider the matter distribution located at thin-shell associated with a scalar field and analyze its effects on the dynamics of thin-shell through equations of motion and effective potential. The corresponding dynamical equations are numerically studied for both massless as well as massive scalar fields. For rotating case, the rate of expansion and collapse increases with massless scalar shell but decreases for massive case. For charged rotating, the rate of expansion and collapse decreases by increasing angular momentum for both massless as well as massive case. We conclude that the rate of expansion and collapse of the rotating case is greater than charged rotating black hole. [ABSTRACT FROM AUTHOR]

The aim of this paper is to study the gravitational collapse of charged cylindrical star in f (𝒢) gravity. For this purpose, we derive dynamical equations by applying Misner–Sharp formalism and examine the effects of effective pressure and charge on the collapse rate. We also construct a relationship between matter variables, Gauss–Bonnet (GB) terms, and the Weyl tensor. For the constant value of f (𝒢) , it is found that spacetime is conformally flat if and only if the energy density is homogeneous. We conclude that the rate of collapse slows down in f (𝒢) gravity due to anti-gravitational effects. [ABSTRACT FROM AUTHOR]

In this paper, we study the importance of configurations of the observer's congruences in the analysis of the dynamical properties of planar relativistic systems in f (R) geometry. To this end, we assume a relativistic distribution of matter contents whose gravitational effects would produce planar geometry. In order to relate matter ingredients seen by tilted and non-tilted observers, we have calculated particular theoretical relationships. After calculating dynamical, Ellis and transport equations, the pace of gravitational collapse as well as the corresponding stable epochs of the systems are discussed. The instability of non-comoving reference frame has been elaborated in a particular background. [ABSTRACT FROM AUTHOR]

Study of gravitational collapse and black hole formation has got much interest in recent years after gravitational waves detection from mergers of black hole binaries. Here, we studied the gravitational collapse of a spherically symmetric clump of matter, constituted of dust fluid, ρ M , in a background of dark energy, ρ. We investigate the curvature effect (k = 0 , 1 , − 1) on the gravitational collapsing process. Gravitational collapsing process for two different cases is discussed i.e. collapse of dust cloud only and collapse of dark energy. We used equation of state p = ω ρ , ω < − 1 / 3. For dark energy case, we discuss the collapsing process and curvature effect for different parameter values of equation of state. [ABSTRACT FROM AUTHOR]

We explore the problem of charged perfect fluid spherically symmetric gravitational collapse in f(R, T) gravity (R is Ricci scalar and T is the trace of energy–momentum tensor). We have taken the interior boundary of a star as spherically symmetric metric filled with the charged perfect fluid. In order to study charged perfect fluid collapse, we have investigated the exact solutions of the Maxwell–Einstein field equations solutions using the most simplified form for f(R, T) model f(R, T) = R + 2 λ T, where λ is model parameter. This study involves the effects of charge as well as coupling parameter on collapse of a star. We studied the nature of trapped surfaces, apparent horizon and singularity structure in detail. It has been found that singularity is formed earlier than the apparent horizons, so the end state of gravitational collapse in this case is black hole. [ABSTRACT FROM AUTHOR]

In this work, we have studied the effects of dissipative viscous/heat gravitational collapse on the dynamics of collapsing source in 5D Einstein–Gauss–Bonnet theory using full casual approach. For this purpose, the dynamical equations have been formulated by using Misner–Sharp approach in 5D Einstein–Gauss–Bonnet theory of gravity. Using the Müller–Israel–Stewart theory, the dynamical equations have coupled with casual transport equations for the heat flux, the bulk and shear bulk viscosity to determine the effects of heat flux including thermodynamics viscous/heat coupling coefficients. The applications of this work to certain astrophysical situations are discussed. [ABSTRACT FROM AUTHOR]

In this research paper, we address the issues of expansion and gravitational collapse of anisotropic spherical source in the presence of cosmological constant. For this purpose, we have solved the Einstein field equations with gravitating source and cosmological constant. The absence of radial heat flux in the gravitating source provide the parametric form of two-metric functions in terms of a single-metric function. The expansion scalar and the mass function of the gravitating source is evaluated for the given metric. The trapping condition is applied to mass function which implies the existence of horizons, like the horizons of Schwarzschild de-Sitter black holes. The trapping condition provides the parametric form of the unknown metric function. The value of expansion scalar has been analyzed in detail to see its positivity and negativity, which correspond to expansion and collapse, respectively. So, the values of parameter α for which expansion scalar is positive have been used to analyze the other physical variables including density, pressures and anisotropy. The same quantities have been evaluated for the values of α that result in the negative values of expansion scalar leading to collapse. The effects of positive cosmological constant have been noted in both expansion and collapse solutions. Due to the presence of cosmological constant after collapse, there would occur inner and outer horizons or a unique horizon depending on the value of mass of the gravitating source. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to discuss the perfect fluid gravitational collapse in modified f(R) metric gravity theories with non-minimal curvature coupled to matter. For this inference, we investigate the effects on self-gravitating implosion with spherically symmetric non-static geometry in the presence of extra force [ 1 + λ f 2 (R) ] L m , that express the cosmic expansion with dark source constraints. Matching conditions are given in which we have taken the insertion of non-static interior and static exterior regions along with cosmological constant. We have investigated the apparent horizons with effective results and along with their physical interpretation. It is analyzed that the extra component of dark source material reduces the gravitating implosion, hence slowing the rate of collapse. This study also reflects the contribution towards the perfect fluid for the generalization in f(R) gravity with zero coupling constant λ. [ABSTRACT FROM AUTHOR]

In the scenario of an optimal consideration that is, homogeneous and flat spacetime, we study the Black Hole (BH) formation from the gravitational collapse of a spherical symmetric clump of matter in the case of the specific Dark Matter (DM) model interacting with Dark Energy (DE) in the context of the brane world regime. This clump of matter constituted of DM, ρ M and DE, ρ. In the present model, we consider anisotropic pressure in the energy–momentum tensor with a polytropic equation of state (EoS), p r = k ρ and p t = ω ρ , ( k + 2 ω < − 1 ). Our results show that the gravitational collapse of an interacting combination of DM and DE leads to the formation of BH in the presence of brane tension. Recent work provides the generalization of isotropic pressure to an-isotropic pressure in the energy–momentum tensor for the specific interacting combination model of DM and DE in a brane world regime. [ABSTRACT FROM AUTHOR]

This paper studies the gravitational collapse of charged anisotropic spherical stellar objects in f(𝒢) gravity. For this purpose, we derive dynamical equations by considering Misner–Sharp mechanism and explore physical impact of charge, anisotropy and effective pressure on the rate of collapse. We establish the relationship between matter variables, Weyl tensor and the Gauss–Bonnet (GB) terms. For constant value of f(𝒢), it turns out that conformal flatness condition is no longer valid due to the effect of anisotropic factor in the present scenario. To obtain conformally flat metric, we impose the condition of isotropic matter distribution which provides energy density homogeneity and conformal flatness of the metric. We conclude that GB terms lead to decrease in the collapse rate due to their anti-gravitational effects. [ABSTRACT FROM AUTHOR]

In this paper, the shadow and the corresponding naked singularity cast by a Kerr–Sen black hole are studied. It is found that the shadow of a rotating black hole would be a dark zone surrounded by a deformed circle, and the shadow is distorted more away from a circle when the black hole approaches the extremal case. Besides, it is shown that the mean radius of the shadow decreases and distortion parameter increases with the increasing of charge, respectively. However, the mean radius and the distortion parameter vary complicatedly with the change of spin parameter. In the beginning, both observables decrease rapidly with the increasing of specific angular momentum, nevertheless, they increase slightly in the latter part. These results show that there would be a significant effect of the spin on the shadows, which would be of great importance for probing the nature of the black hole. [ABSTRACT FROM AUTHOR]

In this paper, our aim is to study ( n + 2)-dimensional collapse of perfect fluid spherically symmetric spacetime in the context of f( R, T) gravity. The matching conditions are acquired by considering a spherically symmetric non-static ( n + 2)-dimensional metric in the inner region and Schwarzschild ( n + 2)-dimensional metric in the outer region of the star. To solve the field equations for above settings in f( R, T) gravity, we choose the stress-energy tensor trace and the Ricci scalar as constants. It is observed that two physical horizons, namely, cosmological and black hole horizons appear as a consequence of this collapse. A singularity is also formed after the birth of both the horizons. It is also observed that the term f( R0, T0) slows down the collapsing process. [ABSTRACT FROM AUTHOR]

We examine in detail the cosmology based on quantal (Bohmian) trajectories as suggested in a recent study [A. F. Ali and S. Das, Phys. Lett. B 741, 276 (2014)]. We disagree with the conclusions regarding predicting the value of the cosmological constant and evading the Big Bang singularity. Furthermore, we show that the approach of using a quantum corrected Raychaudhuri equation (QRE), as suggested in A. F. Ali and S. Das, Phys. Lett. B 741, 276 (2014), is unsatisfactory, because, essentially, it uses the Raychaudhuri equation (RE), which is a kinematical equation, in order to predict dynamics. In addition, even within this inconsistent framework, the authors have adopted unjustified assumptions and carried out incorrect steps leading to doubtful conclusions. [ABSTRACT FROM AUTHOR]

Christodoulou and Rovelli (CR) have remarked on the large interiors possessed by static black holes. We amplify their remarks, and extend them to the spinning case. [ABSTRACT FROM AUTHOR]

This paper is devoted to investigate the dynamics of the self-gravitating adiabatic and anisotropic source in 5D Einstein Gauss-Bonnet gravity. To this end, the source has been taken as Tolman-Bondi model which preserve inhomogeneity in nature. The field equations, Misner-Sharp mass and dynamical equations have formulated in Einstein Gauss-Bonnet gravity in 5D. The junction conditions have been explored between the anisotropic source and vacuum solution in Gauss-Bonnet gravity in detail. The Misner and Sharp approach has been applied to define the proper time and radial derivatives. Further, these helps to formulate general dynamical equations. The equations show that the mass of the collapsing system increases with the same amount as the effective radial pressure increases. The dynamical system preserves retardation which implies that system under-consideration goes to gravitational collapse. [ABSTRACT FROM AUTHOR]

This paper investigates the phenomenon of gravitational collapse of Lemaitre-Tolman-Bondi (LTB) model in the presence of Brans-Dicke (BD) scalar field with nonzero potential field. We find a class of solutions by taking perfect fluid as well as scalar field and check the validity of weak energy conditions. It turns out that two different types of singularities are formed in the presence of scalar field. We conclude that the end state of gravitational collapse turns out to be a black hole (BH) contrary to general relativity (GR). [ABSTRACT FROM AUTHOR]

The Milky Way is the product of a complex evolution of generations of mergers, collapse, star formation, supernova and collisional heating, radiative and collisional cooling, and ejected nucleosynthesis. Moreover, all of this occurs in the context of the cosmic expansion, the formation of cosmic filaments, dark matter halos, spiral density waves, and emerging dark energy. In this review we summarize observational evidence and discuss recent calculations concerning the formation, evolution nucleosynthesis in the galaxies of the Local Group (LG). In particular, we will briefly summarize observations and simulations for the dwarf galaxies and the two large spirals of the LG. We discuss how galactic halos form within the dark matter filaments that define a super-galactic plane. Gravitational interaction along this structure leads to streaming flows toward the two dominant galaxies in the cluster. These simulations and observations also suggest that a significant fraction of the Galactic halo formed as at large distances and then arrived later along these streaming flows. We also consider the insight provided by observations and simulations of nucleosynthesis both within the galactic halo and dwarf galaxies in the LG. [ABSTRACT FROM AUTHOR]

This paper is devoted to analyze the dynamics of plane symmetric gravitational collapse as well as energy density inhomogeneity in f(G) gravity. The field equations are constructed for dissipative isotropic source and Darmois junction conditions are used to discuss the process of collapse. We use Misner-Sharp mechanism to develop dynamical equation and couple it with transport equation to explore the impact of gravitational force on the collapsing rate. For constant f(G) model, we conclude that the rate of collapse slows down. Finally, we discuss the relationship between the Weyl tensor and physical quantities. [ABSTRACT FROM AUTHOR]

In this paper, the gravitational collapse has been studied in the context of higher-dimensional charged-Vaidya spacetime. It is shown that naked singularity always exists in this case and strong form of cosmic censorship is violated. This work extends the earlier studies on naked singularity formation in higher dimensions. [ABSTRACT FROM AUTHOR]

It is thought that the final product of the gravitational collapse is a Kerr black hole and astronomers have discovered several good astrophysical candidates. While there are some indirect evidences suggesting that the latter have an event horizon, and therefore that they are black holes, a proof that the spacetime around these objects is described by the Kerr geometry is still lacking. Recently, there has been an increasing interest in the possibility of testing the Kerr black hole hypothesis with present and future experiments. In this paper, I briefly review the state-of-the-art of the field, focusing on some recent results and works in progress. [ABSTRACT FROM AUTHOR]

We explore the gravitational collapse of a spherically symmetric dust cloud in the Einstein-Gauss-Bonnet gravity without a cosmological constant, and obtain three families of LTB-like solutions. It is shown that the Gauss-Bonnet term has a profound influence on the nature of singularities, and the global structure of spacetime changes drastically from the analogous general relativistic case. Interestingly, the formation of a naked, massive and uncentral singularity, allowed in five-dimensional spacetime, is forbidden if D≥6. Moreover, such singularity is gravitational strong and a serious counterexample to CCH. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to study the effects of dark energy on dynamics of the collapsing fluid within the framework of metric f(R) gravity. The fluid distribution is assumed to be locally anisotropic and undergoing dissipation in the form of heat flow, null radiations and shear viscosity. For this purpose, we take general spherical symmetric spacetime. Dynamical equations are obtained and also some special solutions are found by considering shearing expansion-free evolution of the fluid. It is found that dark energy affects the mass of the collapsing matter and rate of collapse but does not affect the hydrostatic equilibrium. [ABSTRACT FROM AUTHOR]

In the context of the Randall-Sundrum braneworld, the minimal geometric deformation approach, which has been successfully used to generate exact interior solutions to Einstein's field equations for static braneworld stars with local and nonlocal bulk terms, is used to obtain the braneworld version of the Schwarzschild's interior solution. Using this new solution, the behavior of the Weyl functions is elucidated in terms of the compactness for different stellar distributions. [ABSTRACT FROM AUTHOR]

We study the final outcome of gravitational collapse resulting from the plane symmetric charged Vaidya spacetime. Using the field equations, we show that the weak energy condition is always satisfied by collapsing fluid. It is found that the singularity formed is naked. The strength of singularity is also investigated by using Nolan's method. This turns out to be a strong curvature singularity in Tipler's sense and hence provides a counter example to the cosmic censorship hypothesis. [ABSTRACT FROM AUTHOR]

The entropy and area spectra for D-dimensional Gauss–Bonnet black holes are investigated from two different approaches, which are the quasinormal modes approach developed by Hod, Kunstatter and Maggiore, and the very recent method proposed by Ropotenko. The two methods give the same results, which show that the entropy spectrum of Gauss–Bonnet black holes is equidistantly quantized with spacing ΔS = 2πℏ, while the area spectrum is not equally spaced. [ABSTRACT FROM AUTHOR]

The aim of this paper is to review the recent developments in the phenomenology of quantum gravity at the Large Hadron Collider. We shall pay special attention to four-dimensional models which are able to lower the reduced Planck mass to the TeV region and compare them to models with a large extra-dimensional volume. We then turn our attention to reviewing the emission of gravitons (massless or massive) at the LHC and to the production of small quantum black holes. [ABSTRACT FROM AUTHOR]

We present the topological solutions of Einstein gravity in the presence of a non-Abelian Yang–Mills field. In (n+1) dimensions, we consider the SO(n(n-1)/2-1, 1) semisimple group as the Yang–Mills gauge group, and introduce the black hole solutions with hyperbolic horizon. We argue that the four-dimensional solution is exactly the same as the four-dimensional solution of Einstein–Maxwell gravity, while the higher-dimensional solutions are new. We investigate the properties of the higher-dimensional solutions and find that these solutions in five dimensions have the same properties as the topological five-dimensional solution of Einstein–Maxwell (EM) theory although the metric function in five dimensions is different. But in six and higher dimensions, the topological solutions of EYM and EM gravities with non-negative mass have different properties. First, the singularity of EYM solution does not present a naked singularity and is spacelike, while the singularity of topological Reissner–Nordström solution is timelike. Second, there are no extreme six or higher-dimensional black holes in EYM gravity with non-negative mass, while these kinds of solutions exist in EM gravity. Furthermore, EYM theory has no static asymptotically de Sitter solution with non-negative mass, while EM gravity has. [ABSTRACT FROM AUTHOR]

We show the existence of some bouncing cosmological solutions in the braneworld scenario. More specifically, we consider a dynamical three-brane in the background of Born–Infeld and electrically charged Gauss–Bonnet black hole. We find that, in certain range of parameter space, the brane universe, at least classically, never shrinks to a zero size, resulting in a singularity-free cosmology within the classical domain. [ABSTRACT FROM AUTHOR]

In this paper, the effect of electromagnetic field has been investigated on the spherically symmetric gravitational collapse with the perfect fluid in the presence of positive cosmological constant. Junction conditions between the static exterior and non-static interior spherically symmetric spacetimes are discussed. We study the apparent horizons and their physical significance. It is found that electromagnetic field reduces the bound of cosmological constant by reducing the pressure and hence collapsing process is faster as compared to the perfect fluid case. This work gives the generalization of the perfect fluid case to the charged perfect fluid. Results for the perfect fluid case are recovered. [ABSTRACT FROM AUTHOR]

We evaluate quasinormal mode frequencies for RN black hole spacetimes with cosmic string perturbed by a massless Dirac field, using Pöschl–Teller potential method. We find that only in the case of RN black hole having small charge, the effect due to cosmic string will dominate when perturbed by a negatively charged Dirac field, but if we are perturbing with positively charged Dirac field decay will be less in the case of black hole having cosmic string compared to the RN black hole without string. [ABSTRACT FROM AUTHOR]

Since the discovery of accelerated expansion of the universe, it was necessary to introduce a new component of matter distribution called dark energy. The standard cosmological model considers isotropy of the pressure and assumes an equation of state p = ωρ, relating the pressure p and the energy density ρ. The interval of the parameter ω defines the kind of matter of the universe, related to the fulfillment, or not, of the energy conditions of the fluid. The recent interest in this kind of fluid with anisotropic pressure, in the scenario of the gravitational collapse and star formation, imposes a careful analysis of the energy conditions and the role of the components of the pressure. Here, in this work, we show an example where the classification of dark energy for isotropic pressure fluids is used incorrectly for anisotropic fluids. The correct classification and its consequences are presented. [ABSTRACT FROM AUTHOR]

We give a brief review of our previous works.1,2 We discuss two sets of issues. The first has to do with the possibility of getting a non-supersymmetric dS minimum without the addition of $\overline{D3}$-branes as in KKLT, and axionic slow-roll inflation, in type II flux compactifications. The second has to do with the "Inverse Problem"3 and "Fake Superpotentials"4 for extremal (non)supersymmetric black holes in type II compactifications. We use (orientifold of) a "Swiss Cheese" Calabi–Yau5 expressed as a degree-18 hypersurface in WCP4[1, 1, 1, 6, 9] in the "large-volume-scenario" limit6 for the former. [ABSTRACT FROM AUTHOR]

Recent results show that when nonlinear electrodynamics is considered, the no-scalar-hair theorems in the scalar–tensor theories (STT) of gravity, which are valid for the cases of neutral black holes and charged black holes in the Maxwell electrodynamics, can be circumvented.1,2 What is even more, in the present work, we find new non-unique, numerical solutions describing charged black holes coupled to nonlinear electrodynamics in a special class of scalar–tensor theories. One of the phases has a trivial scalar field and coincides with the corresponding solution in General Relativity. The other phases that we find are characterized by the value of the scalar field charge. The causal structure and some aspects of the stability of the solutions have also been studied. For the scalar–tensor theories considered, the black holes have a single, non-degenerate horizon, i.e. their causal structure resembles that of the Schwarzschild black hole. The thermodynamic analysis of the stability of the solutions indicates that a phase transition may occur. [ABSTRACT FROM AUTHOR]

Wilczek and his collaborators' anomaly cancellation approach is applied to the 3D Schwarzschild- and BTZ-like braneworld black holes induced by the generalized $\mathcal{C}$ metrics in the Randall–Sundrum scenario. Based on the fact that the horizon of braneworld black hole will extend into the bulk spacetime, calculation is done from the bulk generalized $\mathcal{C}$ metrics side and it is shown that this approach also reproduces the correct Hawking radiation for these braneworld black holes. Besides, since this approach does not involve the dynamical equation, it is also shown that the Hawking radiation is only a kinematic effect. [ABSTRACT FROM AUTHOR]

The behavior of a Dirac field in a Schwarzschild black hole spacetime is studied. In this work the Hawking temperature and the absorption cross-section for Schwarzschild black hole placed in Dirac field are calculated, taking into consideration the matter waves reflected from the event horizon. The absorption cross-section σabs in Dirac field is found to be ⅛ of absorption cross-section in scalar field. The emission spectra of Schwarzschild black hole placed in an environment of Dirac field is also obtained. [ABSTRACT FROM AUTHOR]