Gauss-Bonnet Coefficient Research Articles

Thermodynamics, phase transition and Joule–Thomson expansion of 4-D Gauss–Bonnet AdS black hole

In this paper, we explore the thermodynamic and phase transition properties of asymptotically AdS black holes within Einstein–Gauss–Bonnet gravity, focusing on Joule–Thomson expansion. Thermodynamics is studied in the extended phase space, where the cosmological constant serves as thermodynamic pressure. We observe that the black hole undergoes a phase transition similar to that of a van der Waals system. We analyze charged and neutral cases separately to distinguish the effect of charge and Gauss–Bonnet parameter on critical behavior and examine the phase structure. We find that the Gauss–Bonnet coupling parameter behaves similarly to black hole charge or spin, guiding the phase structure. To understand the underlying phase structure determined by the Gauss–Bonnet coefficient [Formula: see text], we introduce a new order parameter. We discover that the change in the conjugate variable to the Gauss–Bonnet parameter acts as an order parameter, demonstrating a critical exponent of [Formula: see text] in the vicinity of the critical point. Since the phase structure is analogous to that of a van der Waals fluid, we investigate the Joule–Thomson expansion of the black hole. We analytically study the Joule–Thomson expansion, focusing on three key characteristics: the Joule–Thomson coefficient, inversion curves and isenthalpic curves. We obtain isenthalpic curves in the T–P plane and illustrate the cooling–heating regions.

Wormholes in the axiverse, and the species scale

We analyze a large class of four-dimensional N\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{N} $$\\end{document} = 1 low-energy realizations of the axiverse satisfying various quantum gravity constraints. We propose a novel upper bound on the ultimate UV cutoff of the effective theory, namely the species scale, which only depends on data available at the two-derivative level. Its dependence on the moduli fields and the number N of axions matches expectations from other independent considerations. After an assessment of the regime of validity of the effective field theory, we investigate the non-perturbative gravitational effects therein. We identify a set of axionic charges supported by extremal and non-extremal wormhole configurations. We present a universal class of analytic wormhole solutions, explore their deformations, and analyze the relation between wormhole energy scales and the species scale. The connection between these wormholes and a special subclass of BPS fundamental instantons is discussed, and an argument in favor of the genericity of certain axion-dependent effective superpotentials is provided. We find a lower bound increasing with N ≫ 1 on the Gauss-Bonnet coefficient, resulting in an exponential suppression of non-extremal wormhole effects. Our claims are illustrated and tested in concrete string theory models.

Possibility of the Traversable Wormholes in the Galactic Halos within 4D Einstein–Gauss–Bonnet Gravity

AbstractRecently, there has been significant interest regarding the regularization of a limit of Einstein–Gauss–Bonnet (EGB) gravity. This regularization involves re‐scaling the Gauss–Bonnet (GB) coupling constant as , which bypasses Lovelock's theorem and avoids Ostrogradsky instability. A noteworthy observation is that the maximally or spherically symmetric solutions for all the regularized gravities coincide in the scenario. Considering this, the wormhole solutions in the galactic halos are investigated based on three different choices of dark matter (DM) profiles, such as Universal Rotation Curve, Navarro–Frenk–White, and Scalar Field Dark Matter with the framework of EGB gravity. Also, the Karmarkar condition is used to find the exact solutions for the shape functions under different non‐constant redshift functions. The energy conditions for each DM profile are discussed and the influence of GB coefficient in violating energy conditions are noticed, especially null energy conditions. Further, some physical features of wormholes, viz. complexity factor, active gravitational mass, total gravitational energy, and embedding diagrams, have been explored.

View of thermodynamic phase transition of the charged Gauss–Bonnet AdS black hole via the shadow

We examine thermodynamic phase transition (PT) of the charged Gauss–Bonnet AdS black hole (BH) by utilizing the shadow radius. In this system, we rescale the corresponding Gauss–Bonnet coefficient α by a factor of 1/(D–4), and ensure that α is positive to avoid any singularity problems. The equation derived for the shadow radius indicates that it increases as the event horizon radius increases, making it an independent variable for determining BH temperature. By investigating the PT curve in relation to shadows, we can observe that the shadow radius can be used as an alternative to the event horizon radius in explaining the phenomenon of BH PT. Furthermore, the results indicate that an increase in the parameter α corresponds to a decrease in the temperature of the BH. By utilizing the relationship between the temperature and the shadow radius, it is possible to obtain the thermal profile of the Gauss–Bonnet AdS BH. It is evident that there is an N-type variation in temperature for pressures P < P c. Additionally, as the parameter α increases, the region covered by shadow expands while the temperature decreases. The utilization of BH shadows as a probe holds immense significance in gaining a deeper understanding of BH thermodynamic behavior.

Generating entangled fermions by projective measurements in Gauss–Bonnet spacetime

The properties of the ferimonic entangled states resulting from the projective measurements in the Gauss–Bonnet spacetime are studied. It is found that the degree of entanglement, for projection onto double particles state, increases monotonously as the Hawking temperature T increases but decreases monotonously as the frequency of the detected particles increases; and for projection onto single particle state, the particle states are entangled for spin picture but are separable states for occupation number picture as $$T\rightarrow 0$$ , while the particle states for the both pictures are entangled as $$T\rightarrow \infty $$ . It is also shown that the Gauss–Bonnet coefficient $$\alpha $$ and dimension d of the spacetime will affect the entanglement greatly.

Photon sphere and phase transition of d-dimensional (d ≥ 5) charged Gauss–Bonnet AdS black holes

Motivated by recent work, nonmonotonic behaviors of photon sphere radius can be used to reflect black hole phase transition for Reissner–Nordström–AdS (RN–AdS) black holes, we study the case of five-dimensional charged Gauss–Bonnet–AdS black holes in the reduced parameter space. We find that the nonmonotonic behaviors of photon sphere radius still exist. Using the coexistence line calculated from P–V plane, we capture the photon sphere radius of saturated small and large black holes (the boundary of the coexistence phase), then illustrate the reduced coexistence region. The results show that, reduced coexistence region decreases with charge Q but increases with Gauss–Bonnet coefficient α. When the charge vanishes, reduced coexistence region does not vary with Gauss–Bonnet coefficient α any more. In this case, the Gauss–Bonnet coefficient α plays the same role as the charge of five-dimensional RN–AdS black holes. Also, the situation of higher dimension is studied in the end.

Expanded evasion of the black hole no-hair theorem in dilatonic Einstein-Gauss-Bonnet theory

We study a hairy black hole solution in the dilatonic Einstein-Gauss-Bonnet theory of gravitation, in which the Gauss-Bonnet term is non-minimally coupled to the dilaton field. Hairy black holes with spherical symmetry seem to be easily constructed with a positive Gauss-Bonnet coefficient $\alpha$ within the coupling function, $f(\phi) = \alpha e^{\gamma \phi}$, in an asymptotically flat spacetime, i.e., no-hair theorem seems to be easily evaded in this theory. Therefore, it is natural to ask whether this construction can be expanded into the case with the negative coefficient $\alpha$. In this paper, we present numerically the dilaton black hole solutions with a negative $\alpha$ and analyze the properties of GB term through the aspects of the black hole mass. We construct the new integral constraint allowing the existence of the hairy solutions with the negative $\alpha$. Through this procedure, we expand the evasion of the no-hair theorem for hairy black hole solutions.

Greybody factors for a spherically symmetric Einstein-Gauss-Bonnet–de Sitter black hole

We study the greybody factors of the scalar fields in spherically symmetric Einstein-Gauss-Bonnet-de Sitter black holes in higher dimensions. We derive the greybody factors analytically for both minimally and non-minimally coupled scalar fields. Moreover, we discuss the dependence of the greybody factor on various parameters including the angular momentum number, the non-minimally coupling constant, the spacetime dimension, the cosmological constant and the Gauss-Bonnet coefficient in detail. We find that the non-minimal coupling may suppress the Hawking radiation, while the Gauss-Bonnet coupling could enhance the radiation.

Competing s-wave orders from Einstein–Gauss–Bonnet gravity

In this paper, the holographic superconductor model with two s-wave orders from 4+1 dimensional Einstein–Gauss–Bonnet gravity is explored in the probe limit. At different values of the Gauss–Bonnet coefficient α, we study the influence of tuning the mass and charge parameters of the bulk scalar field on the free energy curve of condensed solution with signal s-wave order, and compare the difference of tuning the two different parameters while the changes of the critical temperature are the same. Based on the above results, it is indicated that the two free energy curves of different s-wave orders can have one or two intersection points, where two typical phase transition behaviors of the s + s coexistent phase, including the reentrant phase transition near the Chern–Simons limit α=0.25, can be found. We also give an explanation to the nontrivial behavior of the Tc–α curves near the Chern–Simons limit, which might be heuristic to understand the origin of the reentrant behavior near the Chern–Simons limit.

Effects of backreaction on power-Maxwell holographic superconductors in Gauss–Bonnet gravity

We analytically and numerically investigate the properties of s-wave holographic superconductors by considering the effects of scalar and gauge fields on the background geometry in five dimensional Einstein-Gauss-Bonnet gravity. We assume the gauge field to be in the form of the Power-Maxwell nonlinear electrodynamics. We employ the Sturm-Liouville eigenvalue problem for analytical calculation of the critical temperature and the shooting method for the numerical investigation. Our numerical and analytical results indicate that higher curvature corrections affect condensation of the holographic superconductors with backreaction. We observe that the backreaction can decrease the critical temperature of the holographic superconductors, while the Power-Maxwell electrodynamics and Gauss-Bonnet coefficient term may increase the critical temperature of the holographic superconductors. We find that the critical exponent has the mean-field value $\beta=1/2$, regardless of the values of Gauss-Bonnet coefficient, backreaction and Power-Maxwell parameters.

Analytical and numerical study of Gauss-Bonnet holographic superconductors with Power-Maxwell field

We provide an analytical as well as a numerical study of the holographic $s$-wave superconductors in Gauss-Bonnet gravity with Power-Maxwell electrodynamics. We limit our study to the case where scalar and gauge fields do not have an effect on the background metric. We use a variational method, based on Sturm-Liouville eigenvalue problem for our analytical study, as well as a numerical shooting method in order to compare with our analytical results. Interestingly enough, we observe that unlike Born-Infeld-like nonlinear electrodynamics which decrease the critical temperature compared to the linear Maxwell field, the Power-Maxwell electrodynamics is able to increase the critical temperature of the holographic superconductors in the sublinear regime. We find that requiring the finite value for the gauge field on the asymptotic boundary $r\rightarrow \infty$, restricts the power parameter, $q$, of the Power-Maxwell field to be in the range $1/2<q<{(d-1)}/{2}$. Our study indicates that it is quite possible to make condensation \emph{easier} as $q$ \emph{decreases} in its allowed range. We also find that for all values of $q$, the condensation can be affected by the Gauss-Bonnet coefficient $\alpha$. However, the presence of the Gauss-Bonnet term makes the transition slightly harder. Finally, we obtain an analytic expression for the order parameter and thus obtain the associated critical exponent near the phase transition. We find that the critical exponent has its universal value of $\beta=1/2$ regardless of the parameters $q$, $\alpha$ as well as dimension $d$, consistent with mean-field values obtained in previous studies.

Noncommutative Wormhole Solutions in Einstein Gauss-Bonnet Gravity

We explore static spherically symmetric wormhole solutions in the framework ofn-dimensional Einstein Gauss-Bonnet gravity. Our objective is to find out wormhole solutions that satisfy energy conditions. For this purpose, we consider two frameworks such as Gaussian distributed and Lorentzian distributed noncommutative geometry. Taking into account constant redshift function, we obtain solutions in the form of shape function. The fifth and sixth dimensional solutions with positive as well as negative Gauss-Bonnet coefficient are discussed. Also, we check the equilibrium condition for the wormhole solutions with the help of generalized Tolman-Oppenheimer-Volkoff equation. It is interesting to mention here that we obtain fifth dimensional stable wormhole solutions in both distributions that satisfy the energy conditions.

P-T phase diagram of a holographic s+p model from Gauss-Bonnet gravity

In this paper, we study the holographic s+p model in 5-dimensional bulk gravity with the Gauss-Bonnet term. We work in the probe limit and give the $\Delta$-T phase diagrams at three different values of the Gauss-Bonnet coefficient to show the effect of the Gauss-Bonnet term. We also construct the P-T phase diagrams for the holographic system using two different definitions of the pressure and compare the results.

Holographic thermalization with a chemical potential in Gauss-Bonnet gravity

Holographic thermalization is studied in the framework of Einstein-Maxwell-Gauss-Bonnet gravity. We use the two-point correlation function and expectation value of Wilson loop, which are dual to the renormalized geodesic length and minimal area surface in the bulk, to probe the thermalization. The numeric result shows that larger the Gauss-Bonnet coefficient is, shorter the thermalization time is, and larger the charge is, longer the thermalization time is, which implies that the Gauss-Bonnet coefficient can accelerate the thermalization while the charge has an opposite effect. In addition, we obtain the functions with respect to the thermalization time for both the thermalization probes at a fixed charge and Gauss-Bonnet coefficient, and on the basis of these functions, we obtain the thermalization velocity, which shows that the thermalization process is non-monotonic. At the middle and later periods of the thermalization process, we find that there is a phase transition point, which divides the thermalization into an acceleration phase and a deceleration phase. We also study the effect of the charge and Gauss-Bonnet coefficient on the phase transition point.

P-V criticality in the extended phase space of Gauss-Bonnet black holes in AdS space

We study the P − V criticality and phase transition in the extended phase space of charged Gauss-Bonnet black holes in anti-de Sitter space, where the cosmological constant appears as a dynamical pressure of the system and its conjugate quantity is the thermodynamic volume of the black holes. The black holes can have a Ricci flat (k = 0), spherical (k = 1), or hyperbolic (k = −1) horizon. We find that for the Ricci flat and hyperbolic Gauss-Bonnet black holes, no P − V criticality and phase transition appear, while for the black holes with a spherical horizon, even when the charge of the black hole is absent, the P − V criticality and the small black hole/large black hole phase transition will appear, but it happens only in d = 5 dimensions; when the charge does not vanish, the P − V criticality and the small black hole/large phase transition always appear in d = 5 dimensions; in the case of d ≥ 6, to have the P − V criticality and the small black hole/large black hole phase transition, there exists an upper bound for the parameter $ b=\widetilde{\alpha }{{\left| Q \right|}^{{{-2 \left/ {{\left( {d-3} \right)}} \right.}}}} $ , where $ \widetilde{\alpha } $ is the Gauss-Bonnet coefficient and Q is the charge of the black hole. We calculate the critical exponents at the critical point and find that for all cases, they are the same as those in the van der Waals liquid-gas system.

Holographic thermalization in Gauss–Bonnet gravity

In the spirit of AdS/CFT correspondence, we study the thermalization of a dual conformal field theory to Gauss–Bonnet gravity by modeling a thin-shell of dust that interpolates between a pure AdS and a Gauss–Bonnet AdS black brane. The renormalized geodesic length and minimal area surface, which in the dual conformal field theory correspond to two-point correlation function and expectation value of Wilson loop, are investigated respectively as thermalization probes. The result shows that as the Gauss–Bonnet coefficient increases, the thermalization time decreases for both the thermalization probes, which can also be confirmed by studying the motion profile of the geodesic and minimal area surface. In addition, for both the renormalized geodesic length and minimal area surface, there is an overlapped region for a fixed boundary separation, which implies that the Gauss–Bonnet coupling constant has little effect on the thermalization probes there.

A soliton and a black hole are in Gauss-Bonnet gravity: Who wins?

We study here the phase-transitional evolution between the Eguchi-Hanson soliton, the orbifolded Schwarzschild Anti de-Sitter black hole, and orbifolded thermal Anti de-Sitter space in Gauss-Bonnet gravity for a small Gauss-Bonnet coefficient $\alpha$. Novel phase structure is uncovered for both negative and positive $\alpha$ with spacetime configurations that are stable in Gauss-Bonnet gravity without being so in Einsteinian gravity. The evolutionary tracks taken towards such stable configurations are guided by quantum tunnelling and can be represented with a phase diagram constructed by comparing the Euclidean actions of each of our states as a function of $\alpha$ and the black hole radius $r_b$. According to the AdS/CFT correspondence dictionary, it is expected that some generalized version of closed-string tachyon condensation will exhibit the phase behaviour found here.

Holographic phase transitions ofp-wave superconductors in Gauss-Bonnet gravity with backreaction

We investigate the phase transitions of holographic $p$-wave superconductors in ($4+1$)-dimensional Einstein-Yang-Mills-Gauss-Bonnet theories, in a grand canonical ensemble. Turning on the backreaction of the Yang-Mills field, it is found that the condensations of vector order parameter become harder if the Gauss-Bonnet coefficient grows up or the backreaction becomes stronger. In particular, the vector order parameter exhibits the features of first order and second order phase transitions, while only the second order phase transition is observed in the probe limit. We discuss the roles that the Gauss-Bonnet term and the backreaction play in changing the order of phase transition.

Thermodynamics of Third Order Lovelock Anti-de Sitter Black Holes Revisited

We compute the mass and temperature of third order Lovelock black holes with negative Gauss—Bonnet coefficient α2 < 0 in anti-de Sitter space and perform the stability analysis of topological black holes. When k = −1, the third order Lovelock black holes are thermodynamically stable for the whole range r+. When k = 1, we found that the black hole has an intermediate unstable phase for D = 7. In eight dimensional spacetimes, however, a new phase of thermodynamically unstable small black holes appears if the coefficient is under a critical value. For D ≥ 9, black holes have similar the distributions of thermodynamically stable regions to the case where the coefficient is under a critical value for D = 8. It is worth to mention that all the thermodynamic and conserved quantities of the black holes with flat horizon do not depend on the Lovelock coefficients and are the same as those of black holes in general gravity.

Holographic p-wave superconductors from Gauss-Bonnet gravity

We study the holographic p-wave superconductors in a five-dimensional Gauss-Bonnet gravity with an SU(2) Yang-Mills gauge field. In the probe approximation, we find that when the Gauss-Bonnet coefficient grows, the condensation of the vector field becomes harder, both the perpendicular and parallel components, with respect to the direction of the condensation, of the anisotropic conductivity decrease. We also study the mass of the quasi-particle excitations, the gap frequency and the DC conductivities of the p-wave superconductor. All of them depend on the Gauss-Bonnet coefficient. In addition we observe a strange behavior for the condensation and the relation between the gap frequency and the mass of quasi-particles when the Gauss-Bonnet coefficient is larger than 9/100, which is the upper bound for the Gauss-Bonnet coefficient from the causality of the dual field theory.