Axion-dilaton Black Holes Research Articles

Dilaton-axion black hole lensing and its relativistic images

Appraising a massive dark object at the centre of our galaxy, we analyse gravitational lensing effect for dilaton-axion black hole. We have explored angular positions, magnifications, time delay, effective deflection angle as well as differential time delay of both primary and secondary first order as well as second order images for such kind of black hole spacetime.

Strong gravitational lensing around dilaton–axion black holes having special coupling with electromagnetic field

Recent observational evidence reveals the existence of black holes in the galaxy. Using strong field lensing effect, we find out the expressions of the radius of the photon sphere, the deflection angle, the separation between the first and the other images, the ratio between the flux of the first image as well as the flux coming from all the other images for dilaton–axion black holes and compare the results with Reissner–Nordstrom black holes. We also investigate the variations of primary and secondary image positions as well as their magnifications with respect to the source position for this kind of black holes.

Komar integral and Smarr formula for axion-dilaton black holes versus S duality

We construct the Komar integral for axion-dilaton gravity using Wald’s formalism and momentum maps and we use it to derive a Smarr relation for stationary axion-dilaton black holes. While the Wald-Noether 2-form charge is not invariant under SL(2, ℝ) electric-magnetic duality transformations because Wald’s formalism does not account for magnetic charges and potentials, the Komar integral constructed with it turns out to be invariant and, in more general theories, it will be fully symplectic invariant. We check the Smarr formula obtained with the most general family of static axion-dilaton black holes.

Examining the weak cosmic censorship conjecture by gedanken experiments for an Einstein–Maxwell–Dilaton–Axion black hole

In the framework of the new version of the gedanken experiments proposed by Sorce and Wald, we investigate the weak cosmic censorship conjecture (WCCC) for an Einstein–Maxwell–Dilaton–Axion (EMDA) black hole. Our result shows that no violations of WCCC can occur with the increase of the background solution parameters for this near-extremal EMDA black hole when the second-order correction of the perturbations is taken into account. Namely, the near-extremal EMDA black hole cannot be over-charged or over-spun.

Dilaton-Axion Black Hole under the Solar System Tests

In the present paper we study the static and spherically symmetric dilaton-axion black hole in the testing ground of the Solar system. We constrain the parameters of the string motivated dilaton-axion form of the classical tests of general relativity, viz., the perihelion precession of the planet Mercury and the deflection of light by the Sun. In this case we have two free parameters: the dilaton strength and the point of curvature singularity of black hole. We obtain the permissible range of these two parameters from theoretical analysis based on the model and later compare them with the observations.

Influence of modified light dispersion theory on fermion tunneling radiation in the Einstein–Maxwell–dilaton–axion black hole**This work was supported by the National Natural Science Foundation of China (grant 11273020), the Sichuan Science and Technology Program (grant 2018JY0502) and the Natural Science Foundation of Shandong Province (grant ZR2019MA059).

Based on a light dispersion relationship derived from string theory and quantum gravitational theory, we make an accurate modification to the quantum tunneling radiation rate and black hole temperature at an event horizon in a stationary axial-symmetric Einstein–Maxwell–dilaton–axion black hole. We also analyze our new results and carry out some significant discussions. This work enriches the research content and methods of the frontiers of black hole physics.

Particles collision near Kerr–Sen Dilaton-Axion black hole

Here, we consider axially symmetric, stationary, rotating and charged Kerr–Sen Dilaton-Axion black hole as particle accelerator. We find the effective potential and discuss the circular orbit of a particle. We investigate the center of mass energy of two colliding neutral particles with different rest masses falling from rest at infinity to near the non-extremal horizons (event horizon and Cauchy horizon) and extremal horizon of the Kerr–Sen Dilaton-Axion black hole. Analogous to the Compton process, we discuss the collision of a particle and a massless photon. Finally, we find the center of mass energy due to the collision of two photons in the background of Kerr–Sen Dilaton-Axion black hole.

Study of superradiant instability of a dilaton-axion black hole under scalar perturbation

We study the superradiant instability of dilaton-axion black holes. For such black holes we examine whether there exists any potential barrier outside the event horizon that can kill the superradiant modes. Our result exhibits that the dilaton-axion couplings do not lead to any superradiant instability under scalar perturbation. This establishes the robustness of superradiant stability for a much wider class of black holes.

Quasi-Local Masses of Rotating Space-Times**Supported by the National Natural Science Foundation of China under Grant No. 11405016, and Basic Research Project of Science and Technology Committee of Chongqing under Grant No. cstc2016jcyja0364

We derive the Misner-Sharp-like masses of the Reissner–Nordström black hole and the Einstein–Maxwell–Dilaton–Axion black hole by using the modified first law of thermodynamics. Their surface tensions are investigated. For the Reissner–Nordström black hole, the outer horizon radius is treated as a variable and the effective temperature is introduced. For the Einstein–Maxwell–Dilaton–Axion black hole, the outer horizon radius, the angular momentum unit mass and the parameter b are seen as three independent variables, and the mass, the horizon area and the angular momentum are functions of them.

Entanglement entropy of charged dilaton-axion black hole and quantum isolated horizon

Based on the work of Ghosh and Perez, we calculate the statistical entropy of charged dilaton-axion black hole. In the calculations we take the integral from the position of QIH to infinity, so the obtained entropy is the entanglement entropy outside the QIH. It is shown that only if the position of QIH is properly chosen the leading term of logarithm of the number of quantum states on the QIH is equal to the leading term of the entanglement entropy outside the black hole horizon, and both are the Bekenstein-Hawking entropy. The results reveal the relation between the entanglement entropy of black hole and the logarithm of the number of quantum states.

Dark Spinors Hawking Radiation in String Theory Black Holes

The Hawking radiation spectrum of Kerr-Sen axion-dilaton black holes is derived, in the context of dark spinors tunnelling across the horizon. Since a black hole has a well defined temperature, it should radiate in principle all the standard model particles, similar to a black body at that temperature. We investigate the tunnelling of mass dimension one spin-1/2 dark fermions, which are beyond the standard model and are prime candidates to the dark matter. Their interactions with the standard model matter and gauge fields are suppressed by at least one power of unification scale, being restricted just to the Higgs field and to the graviton likewise. The tunnelling method for the emission and absorption of mass dimension one particles across the event horizon of Kerr-Sen axion-dilaton black holes is shown here to provide further evidence for the universality of black hole radiation, further encompassing particles beyond the standard model.

The thermodynamical properties of charged dilaton–axion black hole and its quasi-localized energy

We calculate the heat transfer passing through two horizons of charged dilaton–axion black hole and the quasi-localized energy in the patch ℳ between two horizons. The result EEinstein|ℳ= EMø ller|ℳ-∑∂ℳTS is a Legendre transformation. So that the quasi-localized energy EEinsteinand EMø llerin the patch ℳ could be considered as thermodynamic potentials.

Spectroscopies of Extreme Black Holes

The spectroscopies of extreme black holes are investigated by the intrinsic property of these black holes in this paper. We find that the area spectrum of the extreme Reissner-Nordstrom black hole is dependent on the fine structure constant. While the area spectra share the same expression and are determined by the quantum numbers of angular momentum for the extreme Kerr-Sen Dilaton-Axion and Kaluza-Klein black holes.

Spectroscopy of the Einstein–Maxwell–Dilaton–Axion black hole

The entropy spectrum of a spherically symmetric black hole was derived via the Bohr-Sommerfeld quantization rule in Majhi and Vagenas's work. Extending this work to charged and rotating black holes, we quantize the horizon area and the entropy of an Einstein-Maxwell-Dilaton-Axion (EMDA) black hole via the Bohr-Sommerfeld quantization rule and the adiabatic invariance. The result shows the area spectrum and the entropy spectrum are respectively equally spaced and independent on the parameters of the black hole.

Cardy-Verlinde Formula and Thermodynamics of Dilaton-axion Black Hole

In this paper, we have shown that the entropy of the dilaton-axion black hole can be expressed by the Cardy-Verlinde formula. The later is supposed to be an entropy formula of conformal field theory in any dimension. Next we have calculated the first order correction to the Cardy-Verlinde formula in the context of dilaton-axion black hole.

Cardy-Verlinde Formula for an Axially Symmetric Dilaton-axion Black Hole

It is shown that the Bekenstein-Hawking entropy of an axially symmetric dilaton-axion black hole can be expressed as a Cardy-Verlinde formula. By utilizing the first order quantum correction in the Bekenstein-Hawking entropy we find the modified expressions for the Casimir energy and pure extensive energy. The first order correction to the Cardy-Verlinde formula in the context of axially symmetric dilaton-axion black hole are obtained with the use of modified Casimir and pure extensive energies.

Absorption Cross Section and Decay Rate of Stationary Axisymmetric Einstein–Maxwell Dilaton Axion Black Hole

The low energy absorption cross section and the decay rate of the stationary Axisymmetric Einstein–Maxwell Dilaton Axion black hole for massless scalar particles is calculated analytically. It is shown that the partial absorption cross section increases as the rotating parameter a and the absolute value of the dilaton D decreases. It is also shown that the partial absorption cross section is not always positive due to superradiance factor ω–mΩ. However, the decay rate of this black hole is always positive.

Quantum corrections to the entropy of Einstein–Maxwell dilaton–axion black holes

We study the corrections to the entropy of Einstein-Maxwell dilaton-axion black holes beyond semiclassical approximations. We consider the entropy of the black hole as a state variable and derive these corrections using the exactness criteria of the first law of thermodynamics. We note that from this general frame-work the entropy corrections for "simpler" black holes like Schwarzschild, Reissner-Nordstr\"{o}m and anti-de Sitter-Schwarzschild black holes follow easily. This procedure gives us the modified area law as well.

Analytical Kerr-Sen dilaton-axion black hole lensing in the weak deflection limit

We investigate analytical gravitational lensing by charged, stationary, axially symmetric Kerr-Sen dilaton-axion black holes in the weak-deflection limit. Approximate solutions to the lightlike equations of motion are present up to and including third-order terms in $M/b$, $a/b$, and ${r}_{\ensuremath{\alpha}}/b$, where $M$ is the black hole mass, $a$ is the angular momentum, ${r}_{\ensuremath{\alpha}}={Q}^{2}/M$, $Q$ being the charge and $b$ is the impact parameter of the light ray. We compute the positions of the two weak field images, the corresponding signed and absolute magnifications up to post-Newtonian order. It is shown that there are static post-Newtonian corrections to the signed magnification and their sum as well as to the critical curves, which are functions of the charge. The shift of the critical curves as a function of the lens angular momentum is found, and it is shown that they decrease slightly with the increase of the charge. The pointlike caustics drift away from the optical axis and do not depend on the charge. All of the lensing quantities are compared to particular cases as Schwarzschild and Kerr black holes as well as the Gibbons-Maeda-Garfinkle-Horowitz-Strominger black hole.

Entropy of charged dilaton-axion black hole with minimal length revisited

Abstract Using the generalized uncertainty principle, we calculate the entropy of the charged dilaton-axion black hole for both asymptotically flat and non-flat cases by counting degrees of freedom near the horizon. The divergence of density of states and free energy appearing in the thin film brick-wall model is removed without any cutoff. The entropy proportional to the horizon area is derived from the contribution of the vicinity of the horizon.