Gauss-Bonnet Coupling Parameter Research Articles

ЭФФЕКТ САНЬЯКА В ПРОСТРАНСТВЕ-ВРЕМЕНИ ВРАЩАЮЩЕЙСЯ ЧЕРНОЙ ДЫРЫ В ЧЕТЫРЕХМЕРНОЙ ТЕОРИИ ЭЙНШТЕЙНА–ГАУССА–БОННЕ

Recently, Glavan and Lin proposed a new four-dimensional theory of Einstein-Gauss-Bonnet (EGB) gravity by rescaling the Gauss-Bonnet (GB) coupling constant ߙ→ ܦ(/ߙ− 4) and adopting the ܦ→ 4 constraint at the level of the equations of motion. The GB coupling constant contributes to the field equations and thus bypasses Lovelock's theorem. This theory preserves the number of degrees of freedom and avoids Ostrogradsky instability. Glavan and Lin obtained an exact solution for nonsingular static and spherically symmetric black holes in the four-dimensional EGB theory of gravity. Later, Kumar and Ghosh applied the Newman-Janis algorithm to the static solution and constructed a solution for a rotating black hole in the 4-dimensional EGB theory of gravity. Since the theory solves many observational problems in astrophysics and is promising for research, the influence of the GB coupling parameter on astrophysical effects is actively studied in the literature. However, this theory has not been tested previously using time effects. The work examines one of the most interesting time effects – the Sagnac effect. Thus, the goal of the work is to study the Sagnac effect in the space-time of a rotating black hole in the four-dimensional EGB theory and obtain a constraint on the GB coupling parameter using observational data of the Sagnac effect. In the most general case, the Sagnac effect is understood as the difference in the time it takes light beams moving in opposite directions to pass through a closed circle. The effect has many applications, is observable on Earth and is taken into account in satellite navigation systems (GPS, GLONASS) when synchronizing time signals.

Quasinormal modes of Einstein–scalar–Gauss–Bonnet black holes

In this paper, we investigate quasinormal modes of scalar and electromagnetic fields in the background of Einstein–scalar–Gauss–Bonnet (EsGB) black holes. Using the scalar and electromagnetic field equations in the vicinity of the EsGB black hole, we study nature of the effective potentials. The dependence of real and imaginary parts of the fundamental quasinormal modes on parameter p (which is related to the Gauss–Bonnet coupling parameter α\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\alpha $$\\end{document}) for different values of multipole numbers l are studied. We analyzed the effects of massive scalar fields on the EsGB black hole, which tells us the existence of quasi-resonances. In the eikonal regime, we find the analytical expression for the quasinormal frequency and show that the correspondence between the eikonal quasinormal modes and null geodesics is valid in the EsGB theory for the test fields. Finally, we study grey-body factors of the electromagnetic fields for different multipole numbers l, which deviates from Schwarzschild’s black hole.

Celestial attributes of hybrid star in [formula omitted] Einstein-Gauss–Bonnet gravity

Hybrid star is the term given to a neutron star with a quark core. Due to a lot of uncertainties in the calculations and compositions of such a high-density system, it is of great interest and a preferred scenario for particle physicists and astrophysicists. To explore some novel aspects within the framework of the 5D Einstein-Gauss–Bonnet(EGB) gravity, our current study presents a hybrid star model that includes strange quark matter in addition to regular baryonic matter. In hybrid stellar objects, a hadronic outer component surrounds a quark inner component, which prompts the consideration of the most basic MIT bag model equation of state to correlate the density and pressure of strange quark matter within the stellar interior, while radial pressure and matter density due to baryonic matter are connected by a linear equation of state. The model is constructed within the specifications of the Krori and Barua (KB) ansatz (Krori and Barua, J. Phys. A: Math. Gen. 8,508,1975). Here we present the solution for a particular compact object 4U 1538 - 52 with mass M=0.87±0.07M⊙ and radius R=7.866−0.21+0.21 km. We examine the fundamental physical characteristics of the star, which highlights how the values of matter variables are affected by the Gauss–Bonnet coupling parameter α. Finally, as it meets all the physical requirements for a realistic model, we have come to realize that our present model is realistic.

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.

Black holes in 4D AdS Einstein Gauss Bonnet gravity with power: Yang Mills field

In this paper we construct an exact spherically symmetric black hole solution with a power Yang–Mills (YM) source in the context of 4D Einstein Gauss–Bonnet gravity (4D EGB). We choose our source as \((F_{\mu \nu }^{(a)}F^{\mu \nu (a)})^q\), where q is an arbitrary positive real number. Thereafter we study the horizon structure, thermodynamic issues like thermal stability and black hole phase transition. Our purpose here is to analyse the black hole space-time under the net effect coming from the Gauss–Bonnet coupling parameter \(\alpha \) and the nonlinear parameter q. We then evaluate all important thermodynamic quantities to establish the Smarr formula and the first law of thermodynamics in extended phase space. The behaviour of heat capacity as a function of horizon radius is thoroughly studied to understand the thermal stability of the black hole solution. An interesting phenomena of existence/absence of thermal phase transition occur due to the nonlinearity of YM source. For some values of the parameters, we find that the solution exhibits a first-order phase transition, like a van der Waals fluid. In addition, we also verify Maxwell’s equal area law numerically by crucial analysis of Gibbs free energy as a function of temperature. Moreover, the critical exponents are derived and showed the universality class of the scaling behaviour of thermodynamic quantities near criticality.

Shadow and massless particles around regular Bardeen black holes in 4D Einstein Gauss–Bonnet gravity

In this paper, we study dynamics of massless (photon and neutrino-like) particles in the spacetime of regular Bardeen black hole (BH) in novel four-dimensional Einstein–Gauss–Bonnet (4D EGB) theory. First, we have analyzed the hor properties of the spacetime of the Bardeen BH with respect to the Gauss–Bonnet (GB) coupling parameter [Formula: see text]. Our detailed analysis has shown that the GB coupling parameter is limited by maximum and minimum values at, [Formula: see text] and the extreme value of magnetic charge of the BH depends on the parameter [Formula: see text]. We have explored motion of neutrino-like particles and photons around the Bardeen BH. We have also explored the possibility of mimicking cases of the spin of Kerr BH and charge of Reissner–Nordström BH by the Bardeen charge, providing the same values of impact parameter for photons corresponding to the BH shadow size. Finally, we have investigated spherically infalling accretion and shadow of the Bardeen BHs in 4D EGB theory.

Quasi-periodic oscillation around regular Bardeen black holes in 4D Einstein–Gauss–Bonnet gravity

In this paper, we explore the dynamics of test particles in spacetime around regular Bardeen black holes (BHs) in the novel four-dimensional Einstein–Gauss–Bonnet (4D EGB) theory. First, we analyze properties of the spacetime around the Bardeen BH with respect to the Gauss–Bonnet (GB) coupling parameter [Formula: see text], and we show the range of values of the BH charge and the parameter [Formula: see text] that horizon exists as [Formula: see text] and [Formula: see text], respectively. We also investigate the effects of the magnetic charge of the regular BH on innermost stable circular orbits (ISCOs) radius and efficiency of energy release from infalling test particles to the regular Bardeen BH in 4D EGB gravity. Moreover, fundamental frequencies such as Keplerian and harmonic oscillations are also studied with the applications of quasi-periodic oscillations (QPOs) where we proposed a method to test gravity theories through data from astrophysical observations of twin-peak QPOs in relativistic precession (RP) model. Finally, we show the dependence of the distance from the central BH to the orbit where twin-peak QPOs shine from the spin of Kerr BH, magnetic charge of Bardeen and Reissner–Nordström (RN) BHs, and GB coupling parameter.

Phase transitions in 4D Gauss–Bonnet–de Sitter black holes

We investigate thermodynamic aspects of black holes in the recently formulated four dimensional Gauss-Bonnet theory of gravity, focusing on its asymptotically de Sitter ($\Lambda>0$) solutions. We take a Euclidean path integral approach, where thermodynamic data is fixed at a finite radius `cavity' outside the black hole to achieve equilibrium in the presence of the cosmological horizon. Working in the extended phase space where the cosmological constant is treated as a thermodynamic pressure, we study the phase structure of both uncharged and charged solutions, uncovering a wealth of phenomena. In the uncharged case, black holes are found to undergo either the standard Hawking-Page-like transition to empty de Sitter space or a small-large transition (akin to those seen in charged AdS black holes in pure Einstein gravity) depending on the pressure. We also find a triple point where the radiation, small, and large black hole phases coexist, and a zeroth-order phase transition within a narrow range of Gauss-Bonnet coupling parameter. Reentrant phase transitions between radiation and a small black hole also exist inside a certain parameter range. Similar phenomena are found in the charged case, with the charge parameter playing a role analogous to the Gauss-Bonnet coupling parameter in determining the phase structure.

Thermodynamic corrections of Gauss–Bonnet black hole under general uncertainty principle

In this paper, the thermodynamics of Gauss–Bonnet black hole is investigated. We calculate the analytical solutions of corresponding thermodynamic variables, e.g. the Hawking temperature, entropy of the black hole at its event horizon. In addition, we derive the heat capacity to analyze the thermal stability of the black hole. We also compute the rate of emission in terms of photons through tunneling. By adopting a numerical method to analyze their properties, an obvious phase transition behavior is found. Furthermore, according to the general uncertainty principle, we study the quantum corrections to these thermodynamic quantities and obtain the quantum-corrected entropy containing the logarithmic term. At last, we investigate the effects of the Gauss–Bonnet coupling parameter [Formula: see text] and generalized uncertainty principle parameter [Formula: see text] on the thermodynamics of Gauss–Bonnet black hole.

Charged black hole in 4D Einstein-Gauss-Bonnet gravity: particle motion, plasma effect on weak gravitational lensing and centre-of-mass energy

We study the motion of charged and spinning particles and photons in the 4D charged Einstein-Gauss-Bonnet (EGB) black hole vicinity. We determine the radius of the innermost stable circular orbit (ISCO) for test particles. We show that the combined effect of the Gauss-Bonnet (GB) coupling parameter and black hole charge decreases the ISCO and the radius of the photon sphere. Further, we study the gravitational deflection angle and show that the impact of GB term and black hole charge on it is quite noticeable. We also consider the effect of plasma and find the analytical form of the deflection angle in the case of a uniform and non-uniform plasma. Interestingly we find that the deflection angle becomes larger when uniform plasma is considered in comparison to the case of non-uniform plasma. We also study the center of mass energy (E C.M.) obtained by collision process for non-spinning particles and show that the impact of GB parameter and black hole charge leads to high energy collision. In addition, we also study the E C.M. for the case of spinning particles and show that if the two spinning particles collide near the horizon of 4D charged EGB BH, the E C.M. becomes infinitely high which is in disparity with the non-spinning particles counterpart where E C.M. never grows infinitely. To achieve this, an important role is played by the spinning particle known as the near-critical particle (i.e. a particle with fine-tuned parameters). In order to achieve the unbounded E C.M. from the collision of two spinning particles, the energy per unit mass must be less than unity for a near-critical particle, which means such a particle starts from some intermediate position r > rh and not from infinity.

Shadow cast and center of mass energy in a charged Gauss-Bonnet-AdS black hole

This work is devoted to the exploration of shadow cast and center of mass energy in the background of a 4-dimensional charged Gauss-Bonnet-AdS black hole. On investigating particle dynamics, we have examined black hole’s metric function. Whereas, with the help of null geodesics, we pursue to calculate the celestial coordinates and shadow radius of the black hole. We have made use of the hawking temperature to study the energy emission rate. Moreover, we have explored the center of mass energy and discussed its characteristics under the influence of spacetime parameters. For a better understanding, we graphically represent all of our main findings. The acquired result shows that both charge (Q) and AdS radius (l) decrease the shadow radius, while the Gauss-Bonnet coupling parameter (α) increases the shadow radius in AdS spacetime. On the other hand, both Q and α result in diminishing the shadow radius in asymptotically flat spacetime. Finally, we investigate the energy emission rate and center of mass energy under the influence of Q and α.

Relativistic stars in 4D Einstein-Gauss-Bonnet gravity

In the present paper we investigate the structure of relativistic stars in 4D Einstein-Gauss-Bonnet gravity. The mass-radius relations are obtained for realistic hadronic and for strange quark star equations of state, and for a wide range of the Gauss-Bonnet coupling parameter α. Even though the deviations from general relativity for nonzero values of α can be large enough, they are still comparable with the variations due to different modern realistic equations of state if we restrict ourselves to moderate values of α. That is why the current observations of the neutron star masses and radii alone can not impose stringent constraints on the value of the parameter α. Nevertheless some rough constraints on α can be put. The existence of stable stellar mass black holes imposes √(α) ≲ 2.6 km for α > 0 while the requirement that the maximum neutron star mass should be greater than two solar masses gives √(|α|) ≲ 3.9 km for α < 0. We also present an exact solution describing the structure of relativistic stars with uniform energy density in 4D Einstein-Gauss-Bonnet gravity.

Isotropic compact stars in 4D Einstein–Gauss–Bonnet gravity

Recently it has been proposed that the Gauss–Bonnet coupling parameter of Lovelock gravity may suitably be rescaled in order to admit physically viable models of celestial phenomena such that higher curvature effects are active in standard four dimensions as opposed to the usual higher dimensions. We investigate the consequences of this modification in the context of stellar modelling. The evolution of perfect fluid distributions is governed by the pressure isotropy condition and through stipulation of one of the metric potentials complete models emerge from solutions of the master differential equation. New classes of exact solution with this approach have been reported. One particular model is analysed in detail and shown to comport with elementary physical requirements demanded of realistic compact stars suggesting that the modified theory is not inconsistent with observations.

Constraining gravity with eccentric gravitational waves: projected upper bounds and model selection

Gravitational waves allow us to test general relativity in the highly dynamical regime. While current observations have been consistent with waves emitted by quasi-circular binaries, eccentric binaries may also produce detectable signals in the near future with ground- and space-based detectors. We here explore how tests of general relativity scale with the orbital eccentricity of the source during the inspiral of compact objects up to e ∼ 0.8. We use a new, third post-Newtonian-accurate, eccentric waveform model for the inspiral of compact objects, which is fast enough for Bayesian parameter estimation and model selection, and highly accurate for modeling moderately eccentric inspirals. We derive and incorporate the eccentric corrections to this model induced in Brans–Dicke theory and in Einstein–dilaton–Gauss–Bonnet gravity at leading post-Newtonian order, which suggest a straightforward eccentric extension of the parameterized post-Einsteinian formalism. We explore the upper limits that could be set on the coupling parameters of these modified theories through both a confidence-interval- and Bayes-factor-based approach, using a Markov-Chain Monte Carlo and a trans-dimensional, reversible-jump, Markov-Chain Monte Carlo method. We find projected constraints with signals from sources with e ∼ 0.4 that are one order of magnitude stronger than that those obtained with quasi-circular binaries in advanced LIGO. In particular, eccentric gravitational waves detected at design sensitivity should be able to constrain the Brans–Dicke coupling parameter ω ≳ 3300 and the Gauss–Bonnet coupling parameter α1/2 ≲ 0.5 km at 90% confidence. Although the projected constraint on ω is weaker than other current constraints, the projected constraint on α1/2 is 10 times stronger than the current gravitational wave bound.

Spinning Test Particle in Four-Dimensional Einstein–Gauss–Bonnet Black Holes

In this paper, we investigate the motion of a classical spinning test particle in a background of a spherically symmetric black hole based on the novel four-dimensional Einstein–Gauss–Bonnet gravity [D. Glavan and C. Lin, Phys. Rev. Lett. 124, 081301 (2020)]. We find that the effective potential of a spinning test particle in this background could have two minima when the Gauss–Bonnet coupling parameter α is nearly in a special range −8&lt;α/M2&lt;−2 (M is the mass of the black hole), which means a particle can be in two separate orbits with the same spin-angular momentum and orbital angular momentum, and the accretion disc could have discrete structures. We also investigate the innermost stable circular orbits of the spinning test particle and find that the corresponding radius could be smaller than the cases in general relativity.

Extended thermodynamics and microstructures of four-dimensional charged Gauss-Bonnet black hole in AdS space

The discovery of new four-dimensional black hole solutions presents a new approach to understand the Gauss-Bonnet gravity in low dimensions. In this paper, we test the Gauss-Bonnet gravity by studying the phase transition and microstructures for the four-dimensional charged AdS black hole. In the extended phase space, where the cosmological constant and the Gauss-Bonnet coupling parameter are treated as thermodynamic variables, we find that the thermodynamic first law and the corresponding Smarr formula are satisfied. Both in the canonical ensemble and grand canonical ensemble, we observe the small-large black hole phase transition, which is similar to the case of the van der Walls fluid. This phase transition can also appear in the neutral black hole system. Furthermore, we construct the Ruppeiner geometry, and find that besides the attractive interaction, the repulsive interaction can also dominate among the microstructures for the small black hole with high temperature in a charged or neutral black hole system. This is quite different from the five-dimensional neutral black hole, for which only dominant attractive interaction can be found. The critical behaviors of the normalized scalar curvature are also examined. These results will shed new light into the characteristic property of four-dimensional Gauss-Bonnet gravity.

Gauss–Bonnet Inflation after Planck2018

Abstract We study the primordial perturbations and reheating process in the models where the Gauss–Bonnet (GB) term is nonminimally coupled to the canonical and noncanonical (DBI and tachyon) scalar fields. We consider several potentials and GB coupling terms as power-law, dilaton-like, cosh-type, E-model, and T-model. To seek the observational viability of these models, we study the scalar perturbations numerically and compare the results with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO joint data at 68% CL and 95% CL. We also study the tensor perturbations in confrontation with the Planck2018 TT, TE, EE+lowE+lensing+BK14+BAO+ LIGO, and Virgo2016 joint data at 68% CL and 95% CL. In this regard, we obtain some constraints on the GB coupling parameter β. Another important process in the early universe is the reheating phase after inflation, which is necessary to reheat the universe for subsequent evolution. In this regard, we study the reheating process in these models and find some expressions for the e-folds number and temperature during that era. Considering that from Planck TT, TE, EE+lowEB+lensing data and BICEP2/Keck Array 2014, based on the ΛCDM model, we have n s = 0.9658 ± 0.0038 and r &lt; 0.072, we obtain some constraints on the e-folds number and temperature. From the values of the e-folds number and the effective equation of state and also the observationally viable value of the scalar spectral index, we explore the capability of the models in explaining the reheating phase.

Gravitational quasinormal modes of static Einstein-Gauss-Bonnet anti-de Sitter black holes**Supported by FAPESP (2012/08934-0), National Natural Science Foundation of China (11205254, 11178018, 11375279, 11605015), the Natural Science Foundation Project of CQ CSTC (2011BB0052), and the Fundamental Research Funds for the Central Universities (106112016CDJXY300002, 106112017CDJXFLX0014, CDJRC10300003)

In this paper, we describe quasinormal modes (QNMs) for gravitational perturbations of Einstein-Gauss-Bonnet black holes (BHs) in higher dimensional spacetimes, and derive the corresponding parameters of such black holes in three types of spacetime (flat, de Sitter (dS) and anti-de Sitter (AdS)). Our attention is concentrated on discussing the (in)stability of Einstein-Gauss-Bonnet AdS BHs through the temporal evolution of all types of gravitational perturbation fields (tensor, vector and scalar). It is concluded that the potential functions in vector and scalar gravitational perturbations have negative regions, which suppress quasinormal ringing. Furthermore, the influences of the Gauss-Bonnet coupling parameter α, the number of dimensions n and the angular momentum quantum number l on the Einstein-Gauss-Bonnet AdS BHs quasinormal spectrum are analyzed. The QNM frequencies have greater oscillation and lower damping rate with the growth of α. This indicates that QNM frequencies become increasingly unstable with large α. Meanwhile, the dynamic evolutions of the perturbation field are compliant with the results of computation from the Horowitz and Hubeny method. Because the number of extra dimensions is connected with the string scale, the relationship between α and properties of Einstein-Gauss-Bonnet AdS BHs might be beneficial for the exploitation of string theory and extra-dimensional brane worlds.

Holographic isotropisation in Gauss-Bonnet gravity

We study holographic isotropisation of homogeneous, strongly coupled, non-Abelian plasmas in Gauss-Bonnet gravity with a negative cosmological constant. We focus on small values of the Gauss-Bonnet coupling parameter λGB and linearise the equations of motion around a time-dependent background solution with λGB = 0. We numerically solve the linearised equations and show that the entire time evolution of the pressure anisotropy can be well approximated by the linear in λGB corrections to the quasinormal mode expansion, even in the cases of high anisotropy. We finally show that, quite generally, the time evolution of the pressure anisotropy with the Gauss-Bonnet term is approximately shifted with respect to the evolution without it, with the sign of the shift being directly related to the sign of the λGB parameter. Combined with the observation that negative λGB captures qualitative features of positive gauge coupling corrections, this suggests that the latter generically increase the isotropisation time of strongly coupled plasmas.

Constraining scalar-Gauss-Bonnet inflation by reheating, unitarity, and Planck data

We revisit the inflationary dynamics in detail for theories with Gauss-Bonnet gravity coupled to scalar functions, in light of the Planck data. Considering the chaotic inflationary scenario, we constrain the parameters of two models involving inflaton-Gauss-Bonnet coupling by current Planck data. For non zero inflaton-Gauss-Bonnet coupling $\beta$, an inflationary analysis provides us a big cosmologically viable region in the space of $(m,\beta)$, where $m$ is the mass of inflaton. However, we study further on constraining $\beta$ arising from reheating considerations and unitarity of tree-level amplitude involving we have studied the constraints on $\beta$ arising from reheating considerations and unitarity of tree level amplitude involving $2$ graviton $\rightarrow 2$ graviton ($h h\rightarrow hh$) scattering. Our analysis, particularly on reheating significantly reduces the parameter space of $(m,\beta)$ for all models. he quadratic Gauss-Bonnet coupling parameter turns out to be more strongly constrained than that of the linear coupling. For the linear Gauss-Bonnet coupling function, we obtain $\beta \lesssim 10^3$, with the condition $\beta (m/M_P)^2 \simeq 10^{-4}$. However, study of the Higgs inflation scenario in the presence of Gauss-Bonnet term turned out to be strongly disfavored.