Einstein Gauss Bonnet Research Articles

Traversable thin-shell wormhole in the 4D Einstein–Gauss–Bonnet theory

This work investigates the spherically symmetric thin-shell wormhole solutions in four-dimensional Einstein–Gauss–Bonnet theory and explores their stabilities under radial, linear perturbations. These solutions are typically traversable and characterized by a thin-shell throat in accordance with Israel’s junction conditions. In asymptotically flat and AdS spacetimes with a negative Gauss–Bonnet coupling constant, stable neutral wormholes are encountered when the magnitude of the coupling constant becomes significant. The throats of such wormholes are sustained by ordinary matter and possess finite radii. In asymptotically dS spacetimes, no stable neutral wormhole featuring ordinary matter is observed. On the other hand, for positive Gauss–Bonnet coupling constant, stable thin-shell wormhole solutions can be established when the throats are exclusively supported by exotic matter. Moreover, stable charged wormholes comprised of ordinary matter are found universally in the asymptotically flat, AdS, and dS spacetimes. Unlike their neutral counterparts, the throat radii of such charged wormholes can be arbitrarily small. However, as the charge becomes more significant, such solutions only remain stable when supported by exotic matter.

Self-force effects around charged (2+1)-dimensional BTZ black hole in the Einstein–Gauss–Bonnet gravity

In this paper, we discuss a mode sum regularization method for the self-force acting on a charged test particle moving around a Banados, Teitelboim and Zanelli (BTZ) black hole. First, we have calculated the self-force on each individual mode. Then we evaluated our result by summing up the contribution on each mode. We studied a general scheme for static black holes and then present the result for radial trajectories around [Formula: see text]-dimensional charged BTZ black hole in Einstein–Gauss–Bonnet (EGB) gravity. We find that the parameter which is coupling ([Formula: see text]) GR to Einstein–Gauss–Bonnet gravity has a significant impact on the self-force.

Thermodynamical study of black hole with cloud of strings and quintessence in the 4D Einstein–Gauss–Bonnet context

This paper explores the effects of cloud of strings and quintessence on the thermodynamic features of the 4D Einstein–Gauss–Bonnet (EGB) Black Hole (BH). For this purpose, we have evaluated temperature, entropy, Gibb’s free energy and heat capacity of the 4D EGB BH in the presence of cloud of strings and quintessence. We have also shown the graphical behavior of all these physical quantities for various values of Gauss–Bonnet term [Formula: see text], quintessence [Formula: see text], equation of state parameter [Formula: see text] and cloud of string [Formula: see text].

Five-dimensional Einstein–Gauss–Bonnet gravity compactified and applied to a colour-flavour-locked equation of state

Einstein–Gauss–Bonnet gravity in five dimensions is applied to compact stellar objects, in particular to quark stars obeying a colour-flavour-locked equation of state. Matter under such extreme conditions welcomes the use of higher-order gravity theories or the inclusion of extra dimensions in support of higher-curvature effects. In so doing, we focus on the representation of quantities in higher dimensions in standard four-dimensional spacetime via compactification. Invoking extra compact dimensions from a basic string-theoretic perspective provides for the rationalisation of physical quantities computed in higher dimensions.

Stars and junction conditions in Einstein–Gauss–Bonnet gravity

The junction conditions for a higher dimensional spherically symmetric charged and anisotropic static star are derived in Einstein–Gauss–Bonnet (EGB) gravity with nonvanishing cosmological constant. It is shown that for a timelike boundary hypersurface of zero thickness, the generalised matching conditions across this surface in EGB gravity are satisfied. A sufficient condition is that the Israel-Darmois conditions are valid. Therefore it is possible to generate a complete stellar model in EGB gravity. The interior matches to the exterior higher dimensional charged Boulware–Deser spacetime with cosmological constant. The barotropic radial pressure has to vanish at the boundary of the star which is also the case in general relativity.

A case study of small field inflationary dynamics in the Einstein–Gauss–Bonnet framework in the light of GW170817

We study two of the most theoretically promising models of inflation, namely Natural inflation and Mutated Hilltop inflation, in the Einstein-Gauss Bonnet(EGB) gravity framework. In this work, we try to explore these models keeping observations from GW170817 on the speed of gravitational wave to be equal to the speed of light. This has direct implications on the non-minimal coupling to the Gauss–Bonnet invariant in the action. Thus, the effective potential gets new features. We have not only analysed the inflationary dynamics, but also the reheating dynamics and finally the corresponding energy spectrum of the gravitational wave.

Power spectra of slow-roll inflation in the consistent D → 4 Einstein-Gauss-Bonnet gravity

The slow-roll inflation which took place at extremely high energy regimes is in general believed to be sensitive to the high-order curvature corrections to the classical general relativity (GR). In this paper, we study the effects of the high-order curvature term, the Gauss-Bonnet (GB) term, on the primordial scalar and tensor spectra of the slow-roll inflation in the consistent D → 4 Einstein Gauss-Bonnet (4EGB) gravity. The GB term is incorporated into gravitational dynamics via the re-scaling of the GB coupling constant α → α/(D-4) in the limit D → 4. For our purpose, we calculate explicitly the primordial scalar and tensor power spectra with GB corrections accurate to the next-to-leading order in the slow-roll approximation in the slow-roll inflation by using the third-order uniform asymptotic approximation method. The corresponding spectral indices and their runnings of the spectral indices for both the scalar and tensor perturbations as well as the ratio between the scalar and tensor spectra are also calculated up to the next-to-leading order in the slow-roll expansions. These results represent the most accurate results obtained so far in the literature. In addition, by studying the theoretical predictions of the scalar spectral index and the tensor-to-scalar ratio with Planck 2018 constraint in a model with power-law potential, we show that the second-order corrections are important in future measurements.

Rotating black hole in 4D Einstein–Gauss–Bonnet massive gravity: Shadow and center of mass energy

This work comprises the derivation of a rotating black hole metric by applying the modified Newman-Janis algorithm to a static four dimensional black hole in Einstein-Gauss–Bonnet massive gravity. We choose several parametric values to study the influence of graviton mass m and the Gauss–Bonnet parameter α on the horizon radii and photon sphere’s radii of the rotating and non-rotating black holes, respectively. By considering the Hamilton–Jacobi method, we construct the geodesic equations and by using Bardeen’s procedure of impact parameters, we study the effect of graviton mass on the effective potential, shadow, distortion and energy emission rate. We find that the graviton mass has a very significant effect on the shadow and related physical observables. In the vicinity of the black hole, we investigate the collision of two uncharged particles. We compute the energy of the particles in the center of mass frame for the static and rotating BH cases. Finally, the shadow diameter is compared with Sgr. A* to obtain the constraints on the black hole parameters.

Charged fluids in higher order gravity

We generate the field equations for a charged gravitating perfect fluid in Einstein–Gauss–Bonnet gravity for all spacetime dimensions. The spacetime is static and spherically symmetric which gives rise to the charged condition of pressure isotropy that is an Abel differential equation of the second kind. We show that this equation can be reduced to a canonical differential equation that is first order and nonlinear in nature, in higher dimensions. The canonical form admits an exact solution generating algorithm, yielding implicit solutions in general, by choosing one of the potentials and the electromagnetic field. An exact solution to the canonical equation is found that reduces to the neutral model found earlier. In addition, three new classes of solutions arise without specifying the gravitational potentials and the electromagnetic field; instead constraints are placed on the canonical differential equation. This is due to the fact that the presence of the electromagnetic field allows for a greater degree of freedom, and there is no correspondence with neutral matter. Other classes of exact solutions are presented in terms of elementary and special functions (the Heun confluent functions) when the canonical form cannot be applied.

De Sitter potential in six dimensional Einstein–Gauss–Bonnet isotropic fluids

We present a physically reasonable stellar model in 6-dimensional Einstein–Gauss–Bonnet gravity by prescribing the de Sitter temporal metric potential. The model displays the necessary qualitative features of a compact star model with variable density profile. For a specified parameter space, the model is shown to be well-behaved in the sense that the energy density and pressure are both positive and smooth decreasing functions, with the pressure vanishing on a suitable hyper-surface, thus establishing a finite boundary for the isotropic distribution. Additionally, the model is causal, the energy conditions and adiabatic stability index are all satisfied. The exact solution does not contain the Einstein gravity model by switching off the higher curvature coupling. The model in the standard theory is constructed from the field equations, and its own associated parameter space is determined. The Einstein model displays some undesirable traits, which are eliminated when the higher curvature terms are active.

Quasibound States, Stability and Wave Functions of the Test Fields in the Consistent 4D Einstein–Gauss–Bonnet Gravity

We examine the interaction between quantum test particles and the gravitational field generated by a black hole solution that was recently obtained in the consistent 4-dimensional Einstein–Gauss–Bonnet gravity. While quasinormal modes of scalar, electromagnetic, and Dirac fields have been recently studied in this theory, there is no such study for the quasibound states. Here, we calculate the spectrum of quasibound states for the test fields in a spherically symmetric and asymptotically flat black hole solution in the consistent 4-dimensional Einstein–Gauss–Bonnet gravity. The quasispectrum of resonant frequencies is obtained by using the polynomial condition associated to the general Heun functions. We also discuss the stability of the systems for some values of the Gauss-Bonnet coupling constant.

Electromagnetic quasinormal modes of dyonic AdS black holes with quasitopological electromagnetism in a Horndeski gravity theory mimicking EGB gravity at D → 4

We investigate some properties of a black hole in a Horndeski gravity theory mimicking EGB gravity at [Formula: see text]. Borrowing ideas from quasitopological gravities provide a matter source of dyonic fields, in which the black hole solution carries two charges, electric and magnetic, in the context of the Einstein–Gauss–Bonnet (EGB) gravity. However, due to several limitations of the EGB gravity in [Formula: see text], we consider a Horndeski gravity theory which can mimic EGB gravity in [Formula: see text]. The essential practice used in this paper is the electromagnetic quasinormal modes process, with the goal of discovering the spectrum of such an electromagnetic perturbation over the black hole spacetime. The Wentzel–Kramer–Brillouin (WKB) approximation is used to achieve the desired results. The study shows that both the charges have similar impacts on the quasinormal modes.

Five-dimensional cylindrical anisotropic fluid in Einstein–Gauss–Bonnet gravity

In this paper, we present a static solution for the five-dimensional Einstein–Gauss–Bonnet (EGB) gravitational field equations with a cylindrical symmetry and an anisotropic fluid as a source. We consider whole set of equations in the interior space which sourced by static cylindrical anisotropic fluid and junction conditions required for smoothly matching with exterior space which is a cylindrical vacuum solution of five dimensional EGB equation. We achieve density and pressures as functions of cylindrical radial coordinate and give some graphically analysis under numerical solution.

Quasinormal modes of extended gravity black holes through higher order WKB method

Black hole’s quasinormal frequencies are basically the complex numbers which provide information about the relaxation of perturbations and depend on the characteristics of the spacetime and types of perturbations. In this paper, we evaluate the spectrum of the quasinormal modes of Hayward black hole in Einstein–Gauss–Bonnet gravity, Hayward black hole in anti-de Sitter space (AdS) spacetime, and 4-dimensional black hole in Einstein–Lovelock gravity. By utilizing the 6th-order WKB resonance technique, we examine the quasinormal modes frequencies [Formula: see text] by shifting the charge parameter [Formula: see text] (it is also identified with the cosmological constant), circular harmonic index [Formula: see text], and mass of scalar field [Formula: see text]. We observe that 6th-order WKB method gives quite high accuracy when the multipole number [Formula: see text] is larger than the overtone [Formula: see text]. We observe that real and imaginary components of the quasinormal modes are not linear functions similar to Reisnner–Nordström-AdS. For large values of charge, quasinormal ringing becomes slower to settle down to thermal equilibrium and hence the frequency of the oscillation becomes smaller.

Phases of Rotating Black Objects in d = 5 Einstein–Gauss–Bonnet Theory

We considered several different classes of asymptotically flat, rotating black objects in d=5 Einstein–Gauss–Bonnet (EGB) theory. These are black holes with two equal-magnitude angular momenta, in which case extremal configurations are studied as well. Numerical evidence is also given for the existence of EGB generalizations of the Myers–Perry black holes with a single plane of rotation and of the Emparan–Reall balanced black rings. All solutions approach asymptotically the Minkowski background and present no singularities outside or on the horizon. The numerical results suggest that, for any mass of the solutions and any topology of the horizon, the rotating configurations exist up to a maximal value of the GB coupling constant, while the solutions with a spherical horizon topology still satisfy the Einstein gravity bound on angular momentum.

Dynamical analysis in regularized 4D Einstein–Gauss–Bonnet gravity with non-minimal coupling

We investigate the regularized four-dimensional Einstein–Gauss–Bonnet (4DEGB) gravity with a non-minimal scalar coupling function, which is an extension of the regularized 4DEGB theory. By introducing non-minimal coupling to the Gauss-Bonnet term, we demonstrate the additional contribution to the dynamical equations which is otherwise absent in the dimensionally regularized theory. Furthermore, we analyze the stability of the system by using the dynamical system approach based on fixed points. Then, we consider time evolution to investigate the history of the universe and to constrain observational data to obtain the cosmological parameters of the model.

Phase-Space Analysis of an Einstein–Gauss–Bonnet Scalar Field Cosmology

We perform a detailed study of the phase-space of the field equations of an Einstein–Gauss–Bonnet scalar field cosmology for a spatially flat Friedmann–Lemaître–Robertson–Walker spacetime. For the scalar field potential, we consider the exponential function. In contrast, we assume two cases for the coupling function of the scalar field with the Gauss–Bonnet term: the exponential function and the power–law function. We write the field equations in dimensionless variables and study the equilibrium points using normalized and compactified variables. We recover previous results, but also find new asymptotic solutions not previously studied. Finally, these couplings provide a rich cosmological phenomenology.

Evolution of gravitational radiation from black hole under the influence of Einstein–Gauss–Bonnet gravity

In our work, we compute the 4-dimensional Einstein–Gauss–Bonnet gravity black hole solution by applying the Newman–Janis approach and also examine the Hawking temperature. The generalized uncertainty principle (GUP) is applied to compute the Lagrangian field equation and by using the semi-classical phenomenon, we analyze the modified Hawking temperature. By taking into account the graphical analysis, we check the stable conditions of the black hole with the influence of rotation parameter, charged parameter and quantum gravity parameter. Furthermore, we compute the logarithmic entropy corrections in the background of corrected temperature and standard entropy for corresponding black hole. We study the behavior of different thermodynamics quantities like Helmholtz free energy, internal energy, Gibbs free energy and heat capacity under these fluctuations. In our analysis, we note that these corrections enhance the stability of this system, so, under the effects of these corrections, the considered geometry becomes more stable.

Quasinormal modes and phase structure of regular AdS Einstein–Gauss–Bonnet black holes

In this paper, we present an exact regular black hole solution in Einstein–Gauss–Bonnet coupled with nonlinear matter fields. It is a generalization of a regular Einstein–Gauss–Bonnet black hole in [Formula: see text] [Formula: see text] spacetime. The causal structure of the obtained solution identifies with Boulware–Deser black hole solution, except for the curvature singularity at the center. It incorporates the Boulware–Deser black holes in the absence of deviation parameters. We also study the thermodynamic properties of the solution that satisfies a modified first law of thermodynamics. Furthermore, we discuss the stability of the obtained black hole solution and, in this regard, a double phase transition occurs. Within this context, we find that phase transition exists at the point where the heat capacity diverges and, incidentally, the temperature attains the maximum value. We discuss the fluid nature of the black hole also exhibiting critical points. The quasinormal modes of the black hole solution and their dependencies on Gauss–Bonnet coupling and deviation parameters are also analyzed in terms of null geodesics.

On the gravitational collapse in 4-dimensional Einstein–Gauss–Bonnet gravity

In this paper, we treat 4-dimensional Einstein–Gauss–Bonnet (EGB) gravity as general relativity with an effective stress-energy tensor. We will study the modified Oppenheimer–Snyder–Datt model of the gravitational collapse of a star in a 4-dimensional EGB black hole (BH). The inside geometry of the star is described by the spatially flat Friedmann–Robertson–Walker metric and the matter is distributed uniformly without any pre-assumption about its equation of state. The exterior EGB BH is smoothly matched to the interior geometry without the requirement of any thin shell. This gives the energy density, pressure, and the equation of state of collapsing matter. At the end, we study the time evolution of event and apparent horizons.