Maxwell Gravity Research Articles

Exact rotating black hole solutions for f(R) gravity by modified Newman Janis algorithm

We show that the f(R)-gravity theories with constant Ricci scalar in the Jordan/Einstein frame can be described by Einstein or Einstein–Maxwell gravity with a cosmological term and a modified gravitational constant. To obtain the rotating axisymmetric solutions for the Einstein/Einstein–Maxwell gravity with a cosmological constant, we also propose a modified Newmann–Janis algorithm which involves the non-complexification of the radial coordinate and a complexification of the polar coordinate. Using the duality between the two gravity theories we show that the stationary or static solutions for the Einstein/Einstein–Maxwell gravity with a cosmological constant will also be the solutions for the dual f(R)-gravity with constant Ricci scalar.

Cosmological application of the Maxwell gravity

In this study, we consider a cosmological model for the Maxwell gravity which is constructed by gauging the semi-simple extended Poincaré algebra. Inspired by the Einstein–Yang–Mills theory, we describe the Maxwell gauge field in terms of two additional time-dependent scalar fields. Within the context of a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker universe, we derive the Friedmann equations together with new contributions. Additionally, we examine the modified Friedmann equation to demonstrate how diverse cosmological scenarios can be achieved within this framework. Moreover, we investigate the gauge theory of gravity based on the Maxwell algebra and show that this model leads to the (anti)-de Sitter universe as well as a non-accelerated universe model.

Asymptotically locally flat and AdS higher-dimensional black holes of Einstein–Horndeski–Maxwell gravity in the light of EHT observations: shadow behavior and deflection angle

Unification of gravity with other interactions, achieving the ultimate framework of quantum gravity, and fundamental problems in particle physics and cosmology motivate to consider extra spatial dimensions. The impact of these extra dimensions on the modified theories of gravity has attracted a lot of attention. One way to examine how extra dimensions affect the modified gravitational theories is to analytically investigate astrophysical phenomena, such as black hole shadows. In this study, we aim to investigate the behavior of the shadow shapes of higher-dimensional charged black hole solutions including asymptotically locally flat (ALF) and asymptotically locally AdS (ALAdS) in Einstein–Horndeski–Maxwell (EHM) gravitational theory. We utilize the Hamilton–Jacobi method to find photon orbits around these black holes as well as the Carter approach to formulate the geodesic equations. We examine how extra dimensions, negative cosmological constant, electric charge, and coupling constants of the EHM gravity affect the shadow size of the black hole. Then, we constrain these parameters by comparing the shadow radius of these black holes with the shadow size of M87* supermassive black hole captured by the Event Horizon Telescope (EHT) collaborations. We discover that generally the presence of extra dimensions within the EHM gravity results in reducing the shadow size of higher-dimensional ALF and ALAdS charged black holes, whereas the impact of electric charge on the shadow of these black holes is suppressible. Interestingly, we observe that decreasing the negative cosmological constant, i.e., increasing its absolute value, leads to increase the shadow size of the ALAdS charged higher-dimensional black hole in the EHM gravity. Surprisingly, based on the constraints from EHT observations, we discover that only the shadow size of the four dimensional ALF charged black hole lies in the confidence levels of EHT data, whereas owing to the presence of the negative cosmological constant, the shadow radius of the four, five, and seven dimensional ALAdS charged black holes lie within the EHT data confidence levels.

Complexity of charged anisotropic spherically symmetric fluids in gravity

The previous ideology of complexity factor for the dynamical spheres [Herrera et al 2018, Phys. Rev. D, 98, 104059] is extended for the influence of charge. A dynamical spherically symmetric non-dissipative and dissipative self-gravitating structure is examined in the presence of Maxwell gravity to examine the complexity factor. The pattern of evolution is studied with the minimal complexity constraint. The complexity factor remains the same for the structure of fluid distribution, while we examine homologous constraints for the most basic evolution pattern. We calculate the structure scalars which play an important role in order to understand the fundamental properties of the system. The fluid is geodesic as well as shearing for the dissipative case and there is a large number of solutions. In the non-dissipative fluid distribution, a shear-free, homogeneous and isotropic, geodesic fluid correlates with the evolving homologous and vanishing complexity condition. The implication of the condition of vanishing complexity factor and stability are discussed at the end.

Maxwell extension of f(R) gravity

Inspired by the Maxwell symmetry generalization of general relativity (Maxwell gravity), we have constructed the Maxwell extension of f(R) gravity. We found that the semi-simple extension of the Poincare symmetry allows us to introduce geometrically a cosmological constant term in four-dimensional f(R) gravity. This symmetry also allows the introduction of a non-vanishing torsion to the Maxwell f(R) theory. It is found that the antisymmetric gauge field B^{ab} associated with Maxwell extension is considered as a source of the torsion. It is also found that the gravitational equation of motion acquires a new term in the form of an energy–momentum tensor for the background field. The importance of these new equations is briefly discussed.

Orbits of light rays in (1＋2)-dimensional Einstein–power–Maxwell gravity: Exact analytical solution to the null geodesic equations

We study photon orbits within (1＋2)-dimensional Einstein–Power–Maxwell non-linear electrodynamics assuming a static and circularly symmetric background. An exact analytical solution to the null geodesic equations for light rays is obtained in terms of the Weierstraß function. We investigate in detail the impact of the photon energy, the electric charge of the black hole, and the integration constant (initial condition) on the shape of the orbits.

Five-dimensional electrostatic black holes in a background field

We consider five-dimensional electrostatic solutions to Einstein–Maxwell gravity with two commuting spacelike Killing fields. Taking two distinct reductions from five dimensions to a three-dimensional base space, we write the Einstein–Maxwell equations using some axially symmetric functions on . These equations can be viewed as arising from a harmonic map coupled to three-dimensional gravity with the isometries of the target space of this map revealing a hidden symmetry of this sector of the theory. Depending on the choice of reduction this symmetry then gives rise to two different one-parameter families of transformations corresponding to either charging a black hole or immersing it in a background electric field. We use these transformations to charge a static black Saturn and a static L(n, 1) black lens spacetime and by tuning the strength of the external field, we cure the conical singularities to give new regular solutions. Notably the electrified black lens generated is the first example of a regular black lens in Einstein–Maxwell gravity with topologically trivial asymptotics.

Spherical black holes with minimally coupled scalar cloud/hair in Einstein–Born–Infeld gravity

Previous studies showed that, in the presence of a simple and well-motivated self-interaction scalar potential, asymptotically flat and spherical black holes can carry minimally coupled and charged scalar cloud/hair in Einstein–Maxwell gravity. We extend these studies to Einstein–Born–Infeld gravity to consider the effect of nonlinearity of the electromagnetic field. Series of spherical cloudy/hairy black hole solutions are constructed numerically. Results show that increasing the Born–Infeld coupling constant b will make the domain of existence of the solution shrink or even disappear when b is large enough. This implies that, competing with the gravitation, nonlinearity of the electromagnetic field will make the formation of scalar cloud/hair harder or even impossible.

Charged dust in higher curvature geometry

We analyze the configuration of charged dust in the context of the higher dimensional and higher curvature Einstein–Gauss–Bonnet–Maxwell theory. With the prescription of dust, there remains one more prescription to be made in order to close the system of equations of motion. The choice of one of the metric potentials appears to be the only viable way to proceed. Before establishing exact solutions, we examine conditions for the existence of physically reasonable charged dust fluids. It turns out that the branches of the Boulware–Deser metric representing the exterior gravitational field of a neutral spherically symmetric Einstein–Gauss–Bonnet distribution, serve as upper and lower bounds for the spatial potentials of physically reasonable charged dust in Einstein–Gauss–Bonnet–Maxwell gravity. Some exact solutions for 5 and 6 dimensional charged dust hyperspheres are exhibited in closed form. In particular the Einstein ansatz of a constant temporal potential while defective in 5 dimensions actually generates a model of a closed compact astrophysical object in 6 dimensions. A physically viable 5 dimensional charged dust model is also contrasted with its general relativity counterpart graphically.

Stability analysis of circular orbits around a charged BTZ black hole spacetime in a nonlinear electrodynamics model via Lyapunov exponents

We investigate the existence and stability of both the timelike and null circular orbits for a (2 + 1)-dimensional charged BTZ black hole in Einstein-nonlinear Maxwell gravity with a negative cosmological constant. The stability analysis of orbits is performed to study the possibility of chaos in geodesic motion for a special case of black hole so-called conformally invariant Maxwell spacetime. The computations of both proper time Lyapunov exponent [Formula: see text] and coordinate time Lyapunov exponent [Formula: see text] are useful to determine the stability of these circular orbits. We observe the behavior of the ratio [Formula: see text] as a function of radius of circular orbits for the timelike case in view of different values of charge parameter. However, for the null case, we calculate only the coordinate time Lyapunov exponent [Formula: see text] as there is no proper time for massless test particles. More specifically, we further analyze the behavior of the ratio of [Formula: see text] to angular frequency [Formula: see text], so-called instability exponent as a function of charge [Formula: see text] and parameter related to cosmological constant [Formula: see text] for the particular values of other parameters.

Bianchi I metric solutions with nonminimally coupled Einstein–Maxwell gravity theory

By using Bianchi I type of homogenous and anisotropic background metric having cylindrical symmetry in $x$ direction of a local cartesian coordinates system, we solve metric field equations for a non-minimally coupled Einstein-Maxwell gravity. To do so we choose long wavelength EM waves where spatial dependence of the waves are negligible at the expansion duration. Motivation of this work is study directional effects of the EM vector potential on anisotropy trajectory of the space time expansion scale factor. This problem is checked just for de Sitter inflationary epoch because of its importance in the expansion of the universe. By applying the dynamical system approach we investigate stability nature of the cosmic system in two different cases: (a) direction of the EM vector potential is parallel to $x$ direction of the spacetime and (b) it is perpendicular to $x$ direction. We obtained at stable critical points for some of obtained inflationary solutions the EM waves behave as dark energy in cases $a$ and $b$ where the anisotropy is negligible by expanding of the universe while there are some stable critical points with inflationary stable solutions in case $b$ for which the EM waves behave as baryonic visible matter with non-vanishing anisotropy.

Nonlinear magnetically charged black holes in 4D Einstein–Gauss–Bonnet gravity

In this letter we present an exact spherically symmetric and magnetically charged black hole solution with exponential model of nonlinear electrodynamics (Kruglov, 2017) in the context of 4D Einstein–Gauss–Bonnet (EGB) gravity. We show that our −ve branch, in the limit of GB coupling coefficient α→0 and the nonlinear parameter β→0, reduces to the magnetically charged black hole of Einstein–Maxwell gravity in GR. In addition we study the embedding diagram of the black hole geometry and the thermodynamic properties such as the Hawking temperature and the heat capacity of our black hole solution.

Deforming charged black holes with dipolar differential rotation boundary

Motivated by the recent studies of the novel asymptotically global hbox {AdS}_4 black hole with deformed horizon, we consider the action of Einstein–Maxwell gravity in AdS spacetime and construct the charged deforming AdS black holes with differential boundary. In contrast to deforming black hole without charge, there exists at least one value of horizon for an arbitrary temperature. The extremum of temperature is determined by charge q and divides the range of temperature into several parts. Moreover, we use an isometric embedding in the three-dimensional space to investigate the horizon geometry. The entropy and quasinormal modes of deforming charged AdS black hole are also studied in this paper. Due to the existence of charge q, the phase diagram of entropy is more complicated. We consider two cases of solutions: (1) fixing the chemical potential mu ; (2) changing the value of mu according to the values of horizon radius and charge. In the first case, it is interesting to find there exist two families of black hole solutions with different horizon radii for a fixed temperature, but these two black holes have same horizon geometry and entropy. The second case ensures that deforming charged AdS black hole solutions can reduce to standard RN–AdS black holes.

Exact black hole solutions with nonlinear electrodynamic field

We construct exact black hole solutions to Einstein gravity with nonlinear electrodynamic field. In these solutions, there are, in general, four parameters. They are physical mass, electric charge, cosmological constant and the coupling constant. These solutions differ significantly from the Reissner–Nordström–de Sitter solution in Einstein–Maxwell gravity with a cosmological constant, due to the presence of coupling constant. For example, some of them are endowed with a topological defect on angle [Formula: see text] and the electric charge of some can be much larger or smaller than their mass by varying the coupling constant. On the other hand, these spacetimes are all asymptotically de Sitter (or anti-de Sitter). As a result, their causal structure is similar to the Reissner–Nordström–de Sitter spacetime. Finally, the investigations on the thermodynamics reveal that the coupling constant except for solution-4 has the opposite effect as temperature on the phase, structure of black holes. Concretely, the phase-space changes from single phase to three phases with the decrease of temperature. On the contrary, it changes from three phases to a single phase with the decrease of coupling constant.

Generalized Chern–Simons higher-spin gravity theories in three dimensions

The coupling of spin-3 gauge fields to three-dimensional Maxwell and AdS-Lorentz gravity theories is presented. After showing how the usual spin-3 extensions of the AdS and the Poincaré algebras in three dimensions can be obtained as expansions of sl(3,R) algebra, the procedure is generalized so as to define new higher-spin symmetries. Remarkably, the spin-3 extension of the Maxwell symmetry allows one to introduce a novel gravity model coupled to higher-spin topological matter with vanishing cosmological constant, which in turn corresponds to a flat limit of the AdS-Lorentz case. We extend our results to define two different families of higher-spin extensions of three-dimensional Einstein gravity.

Energy-dependent topological anti-de Sitter black holes in Gauss–Bonnet Born–Infeld gravity

Employing higher curvature corrections to Einstein--Maxwell gravity has garnered a great deal of attention motivated by the high energy regime in quantum nature of black hole physics. In addition, one may employ gravity's rainbow to encode quantum gravity effects into the black hole solutions. In this paper, we regard an energy dependent static spacetime with various topologies and study its black hole solutions in the context of Gauss--Bonnet Born--Infeld (GB--BI) gravity. We study thermodynamic properties and examine the first law of thermodynamics. Using suitable local transformation, we endow the Ricci--flat black hole solutions with a global rotation and study the effects of rotation on thermodynamic quantities. We also investigate thermal stability in canonical ensemble through calculating the heat capacity. We obtain the effects of various parameters on the horizon radius of stable black holes. Finally, we discuss second order phase transition in the extended phase space thermodynamics and investigate the critical behavior.

Horndeski gravity and the violation of reverse isoperimetric inequality

We consider Einstein–Horndeski–Maxwell gravity, together with a cosmological constant and multiple Horndeski axions. We construct charged AdS planar black holes in general dimensions where the Horndeski axions span over the planar directions. We analyze the thermodynamics and obtain the black hole volumes. We show that the reverse isoperimetric inequality can be violated, implying that these black holes can store information more efficiently than the Schwarzschild black hole.

Einstein–Gauss–Bonnet black holes with a perturbative nonlinear electrodynamics: Geometrical thermodynamics

Taking into account the perturbative corrections of Einstein (EN)–Maxwell gravity, we study thermodynamical behavior of the black holes in the context of geometrical thermodynamics (GT). We consider a quadratic Maxwell invariant as a correction of Maxwell theory in electromagnetic viewpoint and Gauss–Bonnet (GB) gravity as a correction of EN theory in gravitational point of view. We study thermodynamical phase transition and show that employing Weinhold, Ruppeiner and Quevedo approaches fails to produce desirable results. Next, Hendi–Panahiyan–Eslam Panah–Momennia (HPEM) metric will be employed in order to study GT of the solutions. We show that this metric is capable of matching all the divergence points of its thermodynamical curvature scalar with phase transition and bound points. Moreover, the effects of the variation of different parameters on phase transition points will be investigated.

Gauss–Bonnet black holes and holographic heat engines beyond large N

Working in the extended black hole thermodynamics where a dynamical cosmological constant defines a thermodynamic pressure p, we study the efficiency of heat engines that perform mechanical work via the pdV terms now present in the First Law. Here the black hole itself is the working substance, and we focus on a judiciously chosen engine cycle. We work in Gauss–Bonnet–Einstein–Maxwell gravity with negative cosmological constant and, using a high temperature expansion, compare the results for these ‘holographic’ heat engines to that of previously studied cases with no Gauss–Bonnet sector. From the dual holographic large N field theory perspective, this amounts to studying the effects of a class of corrections to the efficiency of the cycle.

Thermodynamics of topological black holes in Brans-Dicke gravity with a power-law Maxwell field

In this paper, we present a new class of higher dimensional exact topological black hole solutions of the Brans-Dicke theory in the presence of a power-law Maxwell field as the matter source. For this aim, we introduce a conformal transformation which transforms the Einstein-dilaton-power-law Maxwell gravity Lagrangian to the Brans-Dicke-power-law Maxwell theory one. Then, by using this conformal transformation, we obtain the desired solutions. Next, we study the properties of the solutions and conditions under which we have black holes. Interestingly enough, we show that there is a cosmological horizon in the presence of a negative cosmological constant. Finally, we calculate the temperature and charge and then by calculating the Euclidean action, we obtain the mass, the entropy and the electromagnetic potential energy. We find that the entropy does not respect the area law, and also the conserved and thermodynamic quantities are invariant under conformal transformation. Using these thermodynamic and conserved quantities, we show that the first law of black hole thermodynamics is satisfied on the horizon.