Einstein Maxwell-dilaton Theory Research Articles

Accelerating Kaluza–Klein black hole and Kerr/CFT correspondence

We construct a new solution in the Einstein–Maxwell-dilaton theory describing accelerating, charged, and rotating black hole, i.e. the accelerating Kaluza–Klein black hole. Some properties the spacetime are discussed, such as the electromagnetic fields, the area-temperature product, and the holography according to Kerr/CFT correspondence. As expected, the macroscopic Bekenstein–Hawking entropy for an extremal accelerating Kaluza–Klein black hole can be recovered by using Cardy formula of a two dimensional conformal field theory. An interesting feature is found, namely the area-temperature product is just the one belongs to the vacuum Einstein seed solution.

New exact solutions, thermodynamics and phase transition in the Einstein–Maxwell-dilaton theory

New exact solutions, thermodynamics and phase transition in the Einstein–Maxwell-dilaton theory

Dilaton photoproduction in a magnetic dipole field of pulsars and magnetars

According to Einstein–Maxwell-dilaton theory, the dilaton field varvec{psi } can be produced by electromagnetic fields with non-zero Maxwell invariant. So electromagnetic wave propagating in an external electromagnetic field is a typical source of dilaton radiation. For study dilaton photoproduction in astrophysical conditions it’s interesting to consider plane elliptically polarized electromagnetic wave propagating in the electromagnetic field of magnetic dipole textbf{m} of pulsars and magnetars. The dilation field equation is solved in case |varvec{psi }| {mathbf {ll 1}}. The angular distribution dilaton radiation is studied in every point of space. It’s shown that spectral composition of dilatons is similar to spectral composition of plane electromagnetic wave. Amount of dilaton energy radiated in time and all directions is greatest in condition ({{varvec{B}}}_{textbf{1}}^{textbf{2}}-{{varvec{B}}}_{textbf{2}}^{textbf{2}})({{varvec{m}}}_{{varvec{x}}}^{textbf{2}}-{{varvec{m}}}_{{varvec{y}}}^{textbf{2}})ge 0, where {{varvec{B}}}_{textbf{1}} and {{varvec{B}}}_{textbf{2}} are electromagnetic wave amplitudes along the axes of polarization ellipse. This condition is valid for many neutron star systems.

Horizons of charged dilatonic (anti-)de sitter black holes

We summarize our results on the presence and location of horizons in charged black hole solutions of Einstein–Maxwell-dilaton theory with nontrivial dilaton potentials, asymptotically flat or (anti-)de Sitter, as function of the black hole parameters mass, charge and dilaton coupling strength. We observe that there is a value of latter which separates two regions, one where the black hole is Reissner–Nordström-like from a region where it is Schwarzschild-like. We find that for de Sitter and small nonvanishing of the dilaton coupling parameter, the extremal case is not reached by the solution. We also discuss the attractive or repulsive nature of the leading long distance interaction between two such black holes, or a test particle and one black hole, from a worldline effective field theory point of view.

Logarithmic correction to black hole entropy in universal low-energy string theory models

We calculate the logarithmic correction to the entropy of asymptotically flat and AdS black holes (rotating, non-rotating, charged, and uncharged) embedded in Einstein-Maxwell-dilaton (EMD) theories with U(1)-charged. The leading quantum gravitational corrections are achieved in both extremal and non-extremal limits of black hole temperature by designing a common Euclidean gravity setup that evaluates the “logarithmic term” from one-loop effective actions via heat kernel method-based calculations. EMD theories are universal building blocks of compactified string theory or supergravity models in 4D. For a concrete example, we generalize the entire setup and calculate logarithmic corrections for black holes in U(1)2-charged EMD models intersecting with mathcal{N} = 4 ungauged and gauged bosonic supergravity. In contrast to flat backgrounds, all the AdS4 results are found to be non-topological, providing a wider “infrared window” into the microscopic degrees of freedom of black holes in string theory.

Rotating spacetimes generalizing Lifshitz black holes

We present a spinning black hole solution in d dimensions with a maximal number of rotation parameters in the context of the Einstein–Maxwell-Dilaton theory. An interesting feature of such a solution is that it accommodates Lifshitz black holes when the rotation parameters are set to zero. We verify the rotating nature of the black hole solution by performing the quasi-local analysis of conserved charges and defining the corresponding angular momenta. In addition, we perform the thermodynamical analysis of the black hole configuration, show that the first law of thermodynamics is completely consistent, and obtain a Smarr-like formula. We further study the thermodynamic stability of the constructed solution from a local viewpoint, by computing the associated specific heats, and from a global perspective, by using the so-called new thermodynamic geometry. We finally make some comments related to a pathology found in the causal structure of the obtained rotating black hole spacetime and compute some of its curvature invariants.

Quantum critical diffusion and thermodynamics in Lifshitz holography

We present the full charge and energy diffusion constants for the Einstein-Maxwell dilaton (EMD) action for Lifshitz spacetime characterized by a dynamical critical exponent $z$. Therein we compute the fully renormalized static thermodynamic potential explicitly, which confirms the forms of all thermodynamic quantities including the Bekenstein-Hawking entropy and Smarr-like relationship. All thermodynamics are based on a direct computation of the free energy. Our exact computation demonstrates a modification to the Lifshitz-Ward identity for the EMD theory. For transport, we target our analysis at finite chemical potential and include axion fields to generate momentum dissipation. While our exact results corroborate anticipated bounds, we are able to demonstrate that the diffusivities are governed by the engineering dimension of the diffusion coefficient, $[D]=2\ensuremath{-}z$. Consequently, a $\ensuremath{\beta}$ function defined as the derivative of the trace of the diffusion matrix with respect to the effective lattice spacing changes sign precisely at $z=2$. At $z=2$, the diffusion equation exhibits perfect scale invariance and the corresponding diffusion constant is the pure number $1/{d}_{s}$ for both the charge and energy sectors, where ${d}_{s}$ is the number of spatial dimensions. Further, we find that as $z\ensuremath{\rightarrow}\ensuremath{\infty}$, the charge diffusion constant vanishes, indicating charge localization. Deviation from universal decoupled transport obtains when either the chemical potential or momentum dissipation are large relative to temperature, an echo of strong thermoelectric interactions.

Mass of dyonic black holes and entropy super-additivity

We study extremal static dyonic black holes in four-dimensional Einstein–Maxwell–Dilaton theory, for general values of the constant a in the exponential coupling of the dilaton to the Maxwell kinetic term. Explicit solutions are known only for a = 0, a = 1 and , and for general a when the electric and magnetic charges Q and P are equal. We obtain solutions as power series expansions around Q = P, in terms of a small parameter . Using these, and also solutions constructed numerically, we test a relation between the mass and the charges that had been conjectured long ago by Rasheed. We find that although the conjecture is not exactly correct it is in fact quite accurate for a wide range of the black hole parameters. We investigate some improved conjectures for the mass relation. We also study the circumstances under which entropy super-additivity, which is related to Hawking’s area theorem, is violated. This extends beyond previous examples exhibited in the literature for the particular case of dyonic black holes.

Black holes that repel

The recent observation that black holes in certain Einstein-Maxwell-Dilaton (EMD) theories can violate the entropy super-additivity led to the suggestion that these black holes might repel each other. In this paper, we consider EMD theories with two Maxwell fields $A_i$, with general exponential couplings $\exp(a_i \phi)$ in their kinetic terms. We calculate the gravi-electrostatic force between charged black holes $(m_1,e_1)$ and $(M_2,Q_2)$; the former is sufficiently small and can be treated as a point-like object. We find there is a potential barrier caused by the dilaton coupling at $r_0$ outside the back hole horizon $r_+$, provided that $-a_1 a_2> 2(D-3)/(D-2)$. As the black hole approaches extremality, both $r_+$ and $r_0$ vanish, the barrier becomes infinitesimally thin but infinitely high, and the two black holes repel each other in the whole space. There is no electrostatic force between them; the dilaton is the antigravity agent. Furthermore we find that the exact constraint on $a_1 a_2$ can be derived from the requirements that two-charged extremal black holes have a fusion bomb like mass formula and the violation of entropy super-additivity can occur. The two very different approaches give a consistent picture of the black hole repulsion.

Minimal surfaces and generalized Einstein–Maxwell-dilaton theory

We present novel classes of nonstationary solutions to the five-dimensional generalized Einstein–Maxwell-dilaton theory with cosmological constant, in which the Maxwell’s field and the cosmological constant couple to the dilaton field. In the first class of solutions, the two nonzero coupling constants are different, while in the second class of solutions, the two coupling constants are equal to each other. We find consistent cosmological solutions with positive, negative or zero cosmological constant, where the cosmological constant depends on the value of one coupling constant in the theory. Moreover, we discuss the physical properties of the five-dimensional solutions and the uniqueness of the solutions in five dimensions by showing the solutions with different coupling constants cannot be uplifted to any Einstein–Maxwell theory in higher dimensions.

Hyperscaling violating black holes with spherical and hyperbolic horizons

We present a new family of charged black holes with hyperscaling violating asymptotics and non-trivial horizon topology, for arbitrary Lifshitz exponent z and hyperscaling violation parameter . They are -dimensional analytic solutions to a generalized Einstein–Maxwell–Dilaton theory with an additional vector field supporting spherical or hyperbolic horizons. The hyperbolic solutions are only consistent with the null energy condition for and , which explains why they are absent in the pure Lifshitz case. We further study the (extended) thermodynamics of these black holes, both in the fixed charge and fixed potential ensemble, and find that phase transitions only occur for spherical black holes with and any .

Shadow of charged wormholes in Einstein–Maxwell–dilaton theory

The study of shadow is quite prominent nowadays because of the ongoing Event Horizon Telescope1 observations. We construct the shadow images of charged wormholes in Einstein–Maxwell–dilaton (EMD) theory. The spacetime metric of the charged wormholes contains three charges: magnetic charge P, electric charge Q, and dilaton charge Σ. We evaluate the photon geodesics around the charged wormholes. We also calculate the effective potential and discuss its behavior with angular momentum L and different values of charges P, Q, and Σ. A study of the shadow of charged wormholes reveals that the shadow has an effect of the charges P and Q. The radius of the shadow increases with the magnetic charge P as well as the electric charge Q. We also find that the dilaton charge does not affect the shadow of the charged wormholes.

Hairy binary black holes in Einstein-Maxwell-dilaton theory and their effective-one-body description

In General Relativity and many modified theories of gravity, isolated black holes (BHs) cannot source massless scalar fields. Einstein-Maxwell-dilaton (EMd) theory is an exception: through couplings both to electromagnetism and (non-minimally) to gravity, a massless scalar field can be generated by an electrically charged BH. In this work, we analytically model the dynamics of binaries comprised of such scalar-charged ("hairy") BHs. While BHs are not expected to have substantial electric charge within the Standard Model of particle physics, nearly-extremally charged BHs could occur in models of minicharged dark matter and dark photons. We begin by studying the test-body limit for a binary BH in EMd theory, and we argue that only very compact binaries of nearly-extremally charged BHs can manifest non-perturbative phenomena similar to those found in certain scalar-tensor theories. Then, we use the post-Newtonian approximation to study the dynamics of binary BHs with arbitrary mass ratios. We derive the equations governing the conservative and dissipative sectors of the dynamics at next-to-leading order, use our results to compute the Fourier-domain gravitational waveform in the stationary-phase approximation, and compute the number of useful cycles measurable by the Advanced LIGO detector. Finally, we construct two effective-one-body (EOB) Hamiltonians for binary BHs in EMd theory: one that reproduces the exact test-body limit and another whose construction more closely resembles similar models in General Relativity, and thus could be more easily integrated into existing EOB waveform models used in the data analysis of gravitational-wave events by the LIGO and Virgo collaborations.

Scalar charges and the first law of black hole thermodynamics

We present a variational formulation of Einstein–Maxwell-dilaton theory in flat spacetime, when the asymptotic value of the scalar field is not fixed. We obtain the boundary terms that make the variational principle well posed and then compute the finite gravitational action and corresponding Brown–York stress tensor. We show that the total energy has a new contribution that depends on the asymptotic value of the scalar field and discuss the role of scalar charges for the first law of thermodynamics. We also extend our analysis to hairy black holes in Anti-de Sitter spacetime and investigate the thermodynamics of an exact solution that breaks the conformal symmetry of the boundary.

Cosmic censorship and Weak Gravity Conjecture in the Einstein–Maxwell-dilaton theory

We explore the cosmic censorship in the Einstein–Maxwell-dilaton theory following Wald's thought experiment to destroy a black hole by throwing in a test particle. We discover that at probe limit the extremal charged dilaton black hole could be destroyed by a test particle with specific energy. Nevertheless the censorship is well protected if backreaction or self-force is included. At the end, we discuss an interesting connection between Hoop Conjecture and Weak Gravity Conjecture.

Black hole dynamics in Einstein-Maxwell-dilaton theory

We consider the properties and dynamics of black holes within a family of alternative theories of gravity, namely Einstein-Maxwell-dilaton (EMD) theory. We analyze the dynamical evolution of individual black holes as well as the merger of binary black hole systems. We do this for a wide range of parameter values for the family of EMD theories, investigating, in the process, the stability of these black holes. We examine radiative degrees of freedom, explore the impact of the scalar field on the dynamics of merger and compare with other scalar-tensor theories. We argue that the dilaton can largely be discounted in understanding merging binary systems and that the endstates essentially interpolate between charged and uncharged, rotating black holes. For the relatively small charge values considered here, we conclude that these black hole systems will be difficult to distinguish from their analogs within general relativity.

Uniqueness theorem for static phantom wormholes in Einstein–Maxwell-dilaton theory

We prove a uniqueness theorem for completely regular traversable electrically charged wormhole solutions in the Einstein–Maxwell-dilaton gravity with a phantom scalar field and a possible phantom electromagnetic field. In a certain region of the parameter space, determined by the asymptotic values of the scalar field and the lapse function, the regular wormholes are completely specified by their mass, scalar charge and electric charge. The argument is based on the positive energy theorem applied on an appropriate conformally transformed Riemannian space.

On the motion of hairy black holes in Einstein-Maxwell-dilaton theories

Starting from the static, spherically symmetric black hole solutions in massless Einstein-Maxwell-dilaton (EMD) theories, we build a “skeleton” action, that is, we phenomenologically replace black holes by an appropriate effective point particle action, which is well suited to the formal treatment of the many-body problem in EMD theories. We find that, depending crucially on the value of their scalar cosmological environment, black holes can undergo steep “scalarization” transitions, inducing large deviations to the general relativistic two-body dynamics, as shown, for example, when computing the first post-Keplerian Lagrangian of EMD theories.

Phantom wormholes in Einstein–Maxwell-dilaton theory

In this paper we give an electrically charged traversable wormhole solution for the Einstein–Maxwell-dilaton theory when the dilaton is a phantom field, i.e. it has flipped sign kinetic term appearing in the action. In the limit when the charge is zero, we recover the anti-Fisher solution, which can be reduced to the Bronnikov–Ellis solution under certain choices of integration constants. The equations of motion of this theory share the same S-duality invariance of string theory, so the electrically charged solution is rotated into the magnetically charged one by applying such transformations. The scalar field is topological, so we compute its topological charge, and discuss that under appropriate boundary conditions we can have a lump, a kink, or an anti-kink profile. We determine the position of the throat, and show the embedding diagram of the wormhole. As a physical application, we apply the Gauss–Bonnet theorem to compute the deflection angle of a light-ray that passes close to the wormhole.

Moduli spaces of transverse deformations of near-horizon geometries

We investigate deformations of extremal near-horizon geometries in Einstein–Maxwell–Dilaton theory, including various topological terms, and also in D = 11 supergravity. By linearizing the field equations and Bianchi identities over the compact spatial cross-sections of the near-horizon geometry, we prove that the moduli associated with such deformations are constrained by elliptic systems of PDEs. The moduli space of deformations of near-horizon geometries in these theories is therefore shown to be finite dimensional.