Einstein Gauss Bonnet Research Articles

Bouncing behaviours in four dimensional Einstein Gauss-Bonnet gravity with cosmography and observational constraints

Bouncing behaviours in four dimensional Einstein Gauss-Bonnet gravity with cosmography and observational constraints

Holographic p-Wave Superconductor with Excited States in 4D Einstein–Gauss–Bonnet Gravity

We construct a holographic p-wave superconductor with excited states in the 4D Einstein–Gauss–Bonnet gravity using the Maxwell complex vector field model. In the probe limit, we observe that, the higher curvature correction or the higher excited state can hinder the vector condensate to be formed in the full parameter space, which is different from the holographic s-wave superconductor. Regardless of the choice of the vector mass by selecting the value of m2L2 or m2Leff2, we note that the critical chemical potential becomes evenly spaced for the number of nodes and that the difference of the critical chemical potential between the consecutive states depends on the curvature correction. Moreover, we find that the higher curvature correction or the higher excited state will alter the universal relation of the gap frequency, and the pole and delta function of the conductivity for the excited states can be broadened into the peaks with the finite width as the curvature correction increases.

Thin-shell wormhole under non-commutative geometry inspired Einstein–Gauss–Bonnet gravity

Einstein–Gauss–Bonnet gravity is a generalization of the general relativity to higher dimensions in which the first- and second-order terms correspond to general relativity and Einstein–Gauss–Bonnet gravity, respectively. We construct a new class of five-dimensional (5D) thin-shell wormholes by the ‘Cut–Paste’ technique from black holes in Einstein–Gauss–Bonnet gravity inspired by non-commutative geometry starting with a static spherically symmetric, Gaussian mass distribution as a source and for this structural form of the thin-shell wormhole we have explored several salient features of the solution, viz., pressure–density profile, equation of state, the nature of wormhole, total amount of exotic matter content at the shell. We have also analyzed the linearized stability of the constructed wormhole. From our study we can assert that our model is found to be plausible with reference to the other model of thin-shell wormhole available in literature.

Phase and stability of black strings in Einstein-Gauss-Bonnet theory at large D

The phase and stability of black strings in the Einstein-Gauss-Bonnet (EGB) theory are investigated by using the large D effective theory approach. The spacetime metric and thermodynamics are derived up to the next-to-leading order (NLO) in the 1/D expansion. We find that the entropy current defined by the Iyer-Wald formula follows the second law. As in the Einstein theory, the entropy difference from the total mass produces an entropy functional for the effective theory. Including the NLO correction, we find that for the large Gauss-Bonnet coupling constant αGB, the Gregory-Laflamme instability of uniform black strings needs longer wavelength. Moreover, we show that the critical dimension, beyond which non-uiform black strings becomes more stable than uniform ones, increases as αGB becomes large, and approaches to a finite value for αGB→ ∞.

Spherical gravitational collapse in 4D Einstein–Gauss–Bonnet theory

Spherical gravitational collapse in 4D Einstein–Gauss–Bonnet theory

Properties of relativistic star in 5D Einstein–Gauss–Bonnet gravity

In recent years, there has been a growing interest in stellar modeling in the framework of Einstein–Gauss–Bonnet gravity. In this paper, for a relativistic star in static equilibrium, we invoke the five-dimensional Einstein–Gauss–Bonnet gravity and solve the system by assuming a matter distribution that admits a linear equation of state. We fix the model parameters by matching the interior solution to the exterior Boulware–Deser metric, which facilitates physical analysis of the resultant configuration. We analyze the star’s gross physical properties, which brings to attention the role of the Gauss–Bonnet coupling parameter [Formula: see text] in fine-tuning the values of the matter variables.

Isotropic compact stars in four-dimensional Einstein–Gauss–Bonnet gravity coupled with scalar field: reconstruction of model

It has been suggested that the Einstein–Gauss–Bonnet theory coupled with a scalar field (EGBS) may allow us to obtain physically viable models of celestial phenomena such that the scalar field effect is active in standard four dimensions. We consider the spherically symmetric and static configuration of the compact star and explain the consequences of the EGBS theory in the frame of stellar modeling. In our formulation, for any given static profile of energy density rho with spherical symmetry and the arbitrary equation of state (EoS) of matter, we can construct a model which reproduces the profile. Because the profile of the energy density determines the mass M and the radius R_s of the compact star, an arbitrary relation between the mass M and the radius R_s of the compact star can be realized by adjusting the potential and the coefficient function of the Gauss–Bonnet term in the action of EGBS theory. This could be regarded as a degeneracy between the EoS and the functions characterizing the model, which indicates that the mass–radius relation alone is insufficient to constrain the model. Here, we investigate a novel class of analytic spherically symmetric interior solutions by the polytropic EoS. We discuss our model in detail and show that it is in agreement with the necessary physical conditions required for any realistic compact star, confirming that EGBS theory is consistent with observations.

Isotropic Perfect Fluids in Modified Gravity

We generate the Einstein–Gauss–Bonnet field equations in higher dimensions for a spherically symmetric static spacetime. The matter distribution is a neutral fluid with isotropic pressure. The condition of isotropic pressure, an Abel differential equation of the second kind, is transformed to a first order nonlinear canonical differential equation. This provides a mechanism to generate exact solutions systematically in higher dimensions. Our solution generating algorithm is a different approach from those considered earlier. We show that a specific choice of one potential leads to a new solution for the second potential for all spacetime dimensions. Several other families of exact solutions to the condition of pressure isotropy are found for all spacetime dimensions. Earlier results are regained from our treatments. The difference with general relativity is highlighted in our study.

Collapsing solutions in 4D Einstein–Gauss–Bonnet gravity

This paper explores collapsing solutions of the field equations in the context of 4D Einstein–Gauss–Bonnet (EGB) gravity. We study the effects of GB-term on the energy density, pressure (tangential and radial) and anisotropy of the collapsing system. We consider expansion scalar ([Formula: see text]) to obtain the collapsing solution. Furthermore, we discuss the graphical behavior of the source variables.

4D Einstein–Gauss–Bonnet Gravity Coupled to Modified Logarithmic Nonlinear Electrodynamics

Spherically symmetric solution in 4D Einstein–Gauss–Bonnet gravity coupled to modified logarithmic nonlinear electrodynamics (ModLogNED) is found. This solution at infinity possesses the charged black hole Reissner–Nordström behavior. We study the black hole thermodynamics, entropy, shadow, energy emission rate and quasinormal modes. It was shown that black holes can possess the phase transitions and at some range of event horizon radii black holes are stable. The entropy has the logarithmic correction to the area law. The shadow radii were calculated for variety of parameters. We found that there is a peak of the black hole energy emission rate. The real and imaginary parts of the quasinormal modes frequencies were calculated. The energy conditions of ModLogNED are investigated.

Noncommutative inspired 5D charged black hole in Einstein–Gauss–Bonnet theory

Noncommutative inspired 5D charged black hole in Einstein–Gauss–Bonnet theory

Topological corrections and conformal backreaction in the Einstein Gauss–Bonnet/Weyl theories of gravity at D=4

We investigate the gravitational backreaction, generated by coupling a general conformal sector to external, classical gravity, as described by a conformal anomaly effective action. We address the issues raised by the regularization of the topological Gauss–Bonnet and Weyl terms in these actions and the use of dimensional regularization (DR). We discuss both their local and nonlocal expressions, as possible IR and UV descriptions of conformal theories, below and above the conformal breaking scale. Our discussion overlaps with several recent studies of dilaton gravities – obtained via a certain singular limit of the Einstein–Gauss–Bonnet (EGB) theory – originally introduced as a way to bypass Lovelock’s theorem. We show that nonlocal, purely gravitational realizations of such EGB theories, quadratic in the dilaton field, beside their local quartic forms, are possible, by a finite renormalization of the Euler density. Such nonlocal versions, which are deprived of any scale, can be expanded, at least around flat space, in terms of the combination R Box ^{-1} times multiple variations of the anomaly functional, as pointed out in recent studies at d=4. Similar conclusions can be drawn for the proposed nonlocal EGB theory. The expansion emerges from previous investigations of the anomalous conformal Ward identities that constrain such theories around the flat spacetime limit in momentum space.

Accretion around cloud of strings in 4D Einstein–Gauss–Bonnet black hole

In this paper, we study the accretion process of a charged black hole in the background of cloud of strings in the framework of 4D Einstein–Gauss–Bonnet (EGB) gravity theory. Firstly, the steady spherical accretion process of ideal fluid on 4D cloud of strings EGB black hole is studied from the aspects of the radial velocity, the energy density, the mass accretion rate and the sound speed. Then, the general analytical expressions of the accretion process are determined, and the effects of the black hole parameters on the radial velocity, the energy density, the mass accretion rate and the sound velocity are discussed. When the GB coupling constant increases, the energy density and mass accretion rate increase, and the sound velocity and radial speed decrease. EGB gravity and charge have similar physical effects on the accretion process of black hole.

Observational constraints on maximum mass limit and physical properties of anisotropic strange star models by gravitational decoupling in Einstein–Gauss–Bonnet gravity

ABSTRACT In this work, we are guided by the gravitational wave events GW 170817 and GW 190814 together with observations of neutron stars PSR J1614-2230, PSR J1903+6620, and LMC X-4 to model compact objects within the framework of Einstein–Gauss–Bonnet (EGB) gravity. In addition, we employ the extended gravitational decoupling (EGD) method to explore the impact of anisotropy by varying the decoupling parameter. We model strange quark stars in which the interior stellar fluid obeys the MIT Bag equation of state which represents a degenerated Fermi gas comprising of up, down, and strange quarks. In order to close the system of field equations describing the seed solution, we employ the Buchdahl ansatz for one of the metric functions. The θ sector is solved under the bifurcation: $\epsilon =\theta ^0_0$ and $P_r=\theta ^1_1$ leading to two new families of solutions. In order to test the physical viability of the models, we vary the EGB parameter (α) or the decoupling constant (β) to achieve the observed masses and radii of compact objects. Our models are able to account for low-mass stars for a range of β values while α is fixed. The present models mimic the secondary component of the GW 190814 with a mass range of 2.5–2.67 M⊙ and radii typically of the order of 11.76$^{+0.14}_{-0.19}$ km for large values of the EGB parameter and the decoupling constant. The energy exchange between fluids inside the stellar object is sensitive to model parameters which lead to stable configurations.

Examples of Exact Exponential Cosmological Solutions with Three Isotropic Subspaces in Einstein–Gauss–Bonnet Gravity

We consider $(1+ 8)$- and $(1+10)$-dimensional Einstein-Gauss-Bonnet models with the cosmological $\Lambda$-term. Some new examples of exact solutions with three constant Hubble-like parameters in this model are obtained, governed by three non-coinciding Hubble-like parameters: $H \neq 0$, $h_1$ and $h_2$, obeying $m H + k_1 h_1 + k_2 h_2 \neq 0$, corresponding to factor spaces of dimensions $m\geqslant 3$, $ k_1 > 1$ and $ k_2\geqslant 1$. In this case, the multidimensional cosmological model deals with three factor spaces: the external 3-dimensional "our" world and internal subspaces with dimensions $ (m-3)$, $k_1$ and $k_2$.

Non-exotic wormholes in 4D Einstein–Gauss–Bonnet gravity

In the present paper, we investigate wormholes in 4D-Einstein-Gauss-Bonnet gravity without the requirement of exotic matters. We have taken the radial dependent red-shift function $\phi=\ln \left( {\frac {r_{{0}}}{r}}+1 \right)$ and shape function $b(r)={\frac{r_{0}\ln(r+1)}{\ln({r_0}+1)}}$ as well as anisotropic matter sources through equation of state (EoS) $p_r(r) = \omega \rho(r)$. We examine the energy conditions, flaring out condition, throat condition and anisotropic parameter. The volume integral quantifier is also analyzed to validate the existence and stability of the WH solution. We find, for -ve branch wormhole solutions satisfy the null energy conditions (NEC) throughout the entire space time and +ve branch reduces exactly to Morris-Thorne of GR.

GW170817 Implementation on Einstein-Gauss-Bonnet Theory with Non Minimal and Non Minimal Derivative Coupling

The GW170817 event manifests that gravitational wave velocity is close to thespeed of light. As a result, several theories of gravity are no longer applicable, including EinsteinGauss-Bonnet (EGB) inflation. However, a constraint equation could be applied so that thetheory could produce a viable result. In this study, the EGB inflation is being extended byadding a non-minimal coupling (NMC) and a non-minimal derivative coupling (NMDC). Freeparameters values were evaluated to obtained viability with observational indices. We use powerlaw and exponential Gauss-Bonnet coupling functions. Each model provides observational valuesof ns and r that are compatible with the observations and has its characteristic. It specifiesthe free parameter that controls the alteration of ns and r values. The power-law model iscontrolled by the power m of the Gauss-Bonnet coupling function and the potential integrationconstant, V2. While the exponential model is controlled by the potential integration constant cand the power m of the exponential function. Some approximations do not hold true so that themodels need to be rectified. Apparently, the rectified power-law model is violating null energycondition (NEC), so we also provide the non-violating NEC power-law model.

Black holes in Einstein–Gauss–Bonnet gravity with a background of modified Chaplygin gas

Black holes in Einstein–Gauss–Bonnet gravity with a background of modified Chaplygin gas

Magnetized and Magnetically Charged Particles Motion around Regular Bardeen Black Hole in 4D Einstein Gauss–Bonnet Gravity

In this paper, we study the horizon properties and scalar invariants of the spacetime around a regular black hole (BH) in 4D Einstein Gauss-Bonnet (4D EGB) gravity. It is observed that the presence of both Gauss-Bonnet (GB) coupling and magnetic charge parameters causes the shrinking of the outer horizon. We find that the range of the GB parameter α/M2∈(−0.15869,1), and the extreme value of magnetic charge reaches up to gextr=0.886M, which allows for the existence of a BH horizon, while it is gextr=0.7698M for pure Bardeen BH. We also investigate the dynamics of magnetized particles around the magnetically charged Bardeen BH, assuming the particle’s motion occurs in the equatorial plane in the proper observation frame, and the direction of the magnetic dipole moment of the particles is always kept radially and its magnitude is constant. Moreover, the dynamics of magnetically charged particles are also studied, and it is shown that both the energy and angular momentum of the particles corresponding to circular orbits increases with the increase of their magnetic charge. Finally, we also study collisions of magnetized, electrically neutral, and magnetically charged particles around the Bardeen BHs, where we provide analyses of critical angular momentum that may allow collision of the particles near-horizon radius, producing enormous values of center of mass energy of the collisions.

Cosmology in 5D and 4D Einstein–Gauss–Bonnet gravity

We consider the five-dimensional Einstein–Gauss–Bonnet gravity, which can be obtained by means of an appropriate choice of coefficients in the five-dimensional Lanczos–Lovelock gravity theory. The Einstein–Gauss–Bonnet field equations for the Friedmann–Lemaître–Robertson–Walker metric are found as well as some of their solutions. The hyperbolicity of the corresponding equations of motion is discussed. A four-dimensional gravity action is obtained from the Gauss–Bonnet gravity using the Randall–Sundrum compactification procedure and then it is studied the implications of the compactification procedure in the cosmological solutions. The same procedure is used to obtain gravity in four dimensions from the five-dimensional AdS–Chern–Simons gravity to then study some cosmological solutions. Some aspects of the construction of the four-dimensional action gravity, as well as a brief review of Lovelock gravity in 5D are considered in an Appendix.