Einstein Maxwell Dilaton Axion Research Articles

Chaotic motion of scalar particle coupling to Chern–Simons invariant in the stationary axisymmetric Einstein–Maxwell dilaton black hole spacetime

We investigate the motion of a test scalar particle coupling to the Chern–Simons (CS) invariant in the background of a stationary axisymmetric black hole in the Einstein–Maxwell–Dilaton–Axion (EMDA) gravity. Comparing with the case of a Kerr black hole, we observe that the presence of the dilation parameter makes the CS invariant more complex, and changes the range of the coupling parameter and the spin parameter where the chaotic motion appears for the scalar particle. Moreover, we find that the coupling parameter together with the spin parameter also affects the range of the dilation parameter where the chaos occurs. We also probe the effects of the dilation parameter on the chaotic strength of the chaotic orbits for the coupled particle. Our results indicate that the coupling between the CS invariant and the scalar particle yields the richer dynamical behavior of the particle in the rotating EMDA black hole spacetime.

Constraints on Einstein-Maxwell dilaton-axion gravity from X-ray reflection spectroscopy

Einstein-Maxwell dilaton-axion gravity is a string-inspired model arising from the low energy effective action of heterotic string theory and an important candidate as alternative to General Relativity. Recently, some authors have explored its astrophysical implications in the spectra of accreting black holes and inferred the constraint r2 < 0.1, where r2 ≥ 0 is the black hole dilaton charge and General Relativity is recovered for r2 = 0. In the present paper, we study the impact of a non-vanishing black hole dilaton charge on the reflection spectrum of the disk. From the analysis of a NuSTAR spectrum of the black hole binary EXO 1846-031, we find the constraint r2 < 0.011 (90% CL), which is an order of magnitude more stringent.

Signatures of Einstein-Maxwell dilaton-axion gravity from the observed jet power and the radiative efficiency

The Einstein-Maxwell dilaton-axion (EMDA) gravity arises in the low energy effective action of the heterotic string theory and provides a simple framework to explore the signatures of the same. The dilaton and the axion fields inherited in the action from string compactifications have interesting consequences in inflationary cosmology and in explaining the present accelerated expansion of the universe. It is therefore worthwhile to search for the footprints of these fields in the available astrophysical observations. Since Einstein gravity is expected to receive quantum corrections in the high curvature domain, the near horizon regime of black holes seems to be the ideal astrophysical laboratory to test these deviations from general relativity. Exact, stationary and axisymmetric black hole solution in EMDA gravity corresponds to the Kerr-Sen spacetime which carries dilaton charge, while the angular momentum is sourced by the axion field. The ballistic jets and the peak emission of the continuum spectrum from the accretion disk are believed to be launched very close to the event horizon and hence should bear the imprints of the background spacetime. We compute the jet power and the radiative efficiency derived from the continuum spectrum in the Kerr-Sen background and compare them with the corresponding observations of microquasars. Our analysis reveals that Kerr black holes are more favored compared to Kerr-Sen black holes with dilaton charges.

Lorentz invariance violation and modified Hawking fermions tunneling radiation of stationary axially symmetric black holes

Based on a higher energy scale, the dispersion relation might be corrected. Correspondingly, the Hamilton–Jacobi equation should also be modified. In this paper, we use the correction to study the fermion tunneling radiation for a Gibbons–Maeda–Garfinkle-Horowitz–Strominger (GMGHS) black hole, a Kerr–NUT black hole, and an Einstein–Maxwell–Dilaton–Axion (EMDA) black hole. The result shows that compared to the charged GMGHS black hole and the rotating Kerr–NUT black hole, the Hawking temperate and the entropy of the rotating charged EMDA black hole not only are related to the correction parameter [Formula: see text] and particle mass [Formula: see text] but also depend on the angle parameter [Formula: see text] of the black hole coordinates.

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.

Implications of Einstein–Maxwell dilaton–axion gravity from the black hole continuum spectrum

ABSTRACT String inspired models can serve as potential candidates to replace general relativity (GR) in the high-energy/high-curvature regime where quantum gravity is expected to play a vital role. Such models not only subsume the ultraviolet nature of gravity but also exhibit promising prospects in resolving issues like dark matter and dark energy, which cannot be adequately addressed within the framework of GR. The Einstein–Maxwell dilaton–axion (EMDA) theory that is central to this work is one such string inspired model arising in the low energy effective action of the heterotic string theory with interesting implications in inflationary cosmology and in the late-time acceleration of the Universe. It is therefore important to survey the role of such a theory in explaining astrophysical observations, e.g. the continuum spectrum of black holes which is expected to hold a wealth of information regarding the background metric. The Kerr–Sen space–time corresponds to the exact, stationary, and axisymmetric black hole solution in EMDA gravity, possessing dilatonic charge and angular momentum originating from the axionic field. In this work, we compute the theoretical spectrum from the accretion disc around quasars in the Kerr–Sen background assuming the thin accretion disc model due to Novikov and Thorne. This is then used to evaluate the theoretical estimates of optical luminosity for a sample of eighty Palomar Green quasars which are subsequently compared with the available observations. Our results based on χ2 analysis indicate that the dilaton parameter r2 ∼ 0.2 is favoured by optical observations of quasars which is further corroborated by other error estimators e.g. the Nash–Sutcliffe efficiency, the index of agreement and their modified versions. We further report that strong dilaton charges (r2 &amp;gt; 1.6) are disfavoured by quasar optical data and the spins associated with the quasars are also estimated.

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.

Charged fermions tunneling from stationary axially symmetric black holes with generalized uncertainty principle

In this paper, we study the tunneling of charged fermions from the stationary axially symmetric black holes using the generalized uncertainty principle (GUP) via Wentzel, Kramers, and Brillouin (WKB) method. The emission rate of the charged fermions and corresponding modified Hawking temperature of Kerr–Newman black hole, Einstein–Maxwell-dilaton-axion (EMDA) black hole, Kaluza–Klein dilaton black hole, and then, charged rotating black string are obtained and we show that the corrected thermal spectrum is not purely thermal because of the minimal scale length which cause the black hole’s remnant.

Weyl corrections to diffusion and chaos in holography

Using holographic methods in the Einstein-Maxwell-dilaton-axion (EMDA) theory, it was conjectured that the thermal diffusion in a strongly coupled metal without quasi-particles saturates an universal lower bound that is associated with the chaotic property of the system at infrared (IR) fixed points [1]. In this paper, we investigate the thermal transport and quantum chaos in the EMDA theory with a small Weyl coupling term. It is found that the Weyl coupling correct the thermal diffusion constant DQ and butterfly velocity vB in different ways, hence resulting in a modified relation between the two at IR fixed points. Unlike that in the EMDA case, our results show that the ratio DQ/(vB2τL) always contains a non-universal Weyl correction which depends also on the bulk fields as long as the U(1) current is marginally relevant in the IR.

Magnetothermoelectric DC conductivities from holography models with hyperscaling factor in Lifshitz spacetime

We investigate an Einstein–Maxwell-Dilaton–Axion holographic model and obtain two branches of a charged black hole solution with a dynamic exponent and a hyperscaling violation factor when a magnetic field presents. The magnetothermoelectric DC conductivities are then calculated in terms of horizon data by means of holographic principle. We find that linear temperature dependence resistivity and quadratic temperature dependence inverse Hall angle can be achieved in our model. The well-known anomalous temperature scaling of the Nernst signal and the Seebeck coefficient of cuprate strange metals are also discussed.

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.

Hawking radiation of non-asymptotically flat rotating black holes

We study the Hawking radiation of non-asymptotically flat rotating linear dilaton black holes, which are the solutions to the $4D$ Einstein–Maxwell-dilaton–axion action by using the semi-classical radiation spectrum method. Using scalar perturbations, we show that both angular and radial equations produce exact analytical solutions. Thus, we obtain a precise radiation spectrum for the rotating linear dilaton black hole. The high-frequency regime does not yield the standard Hawking temperature of this black hole computed from the surface gravity. However, we show in detail that the specific low-frequency band of the radiation spectrum allows for the original Hawking temperature of the rotating linear dilaton black hole. The computations are also exhibited graphically.

Quantization of rotating linear dilaton black holes

In this paper, we focus on the quantization of $4-$dimensional rotating linear dilaton black hole (RLDBH) spacetime describing an action, which emerges in the Einstein-Maxwell-Dilaton-Axion (EMDA) theory. RLDBH spacetime has a non-asymptotically flat (NAF) geometry. When the rotation parameter " $a$" vanishes, the spacetime reduces to its static form, the so-called linear dilaton black hole (LDBH) metric. Under scalar perturbations, we show that the radial equation reduces to a hypergeometric differential equation. Using the boundary conditions of the quasinormal modes (QNMs), we compute the associated complex frequencies of the QNMs. In a particular case, QNMs are applied in the rotational adiabatic invariant quantity, and we obtain the quantum entropy/area spectra of the RLDBH. Both spectra are found to be discrete and equidistant, and independent of $a-$parameter despite the modulation of QNMs by this parameter.

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.

BLACK HOLES AND COLLISION ENERGY IN THE CENTER-OF-MASS FRAME

It is shown that in the background of the Ayòn–Beato–Garcìa–Bronnikov (ABGB) black hole, the center-of-mass (CM) energy of collision for two charged particles falling freely from rest at infinity is infinite at the event horizon if one of the colliding particle has critical charge and the other one has any different value of the charge. For the Einstein–Maxwell-dilaton–axion (EMDA) black hole it is found that the CM energy of collision for two uncharged particles falling freely from rest at infinity remains finite. In the case of Bañados–Teitelboim–Zanelli (BTZ) black hole the CM energy of collision for two uncharged particles falling freely from rest at infinity is infinite at the event horizon if there is no rotation. It is observed that in the case of the extremal rotating BTZ black hole, at the event horizon this CM energy remains finite.

Total Energy of Charged Black Holes in Einstein-Maxwell-Dilaton-Axion Theory

We focus on the energy content (including matter and fields) of the Møller energy-momentum complex in the framework of Einstein-Maxwell-Dilaton-Axion (EMDA) theory using teleparallel gravity. We perform the required calculations for some specific charged black hole models, and we find that total energy distributions associated with asymptotically flat black holes are proportional to the gravitational mass. On the other hand, we see that the energy of the asymptotically nonflat black holes diverge in a limiting case.

All extremal instantons in Einstein-Maxwell-dilaton-axion theory

We construct explicitly all extremal instanton solutions to $\mathcal{N}=4,\, D=4$ supergravity truncated to one vector field (Einstein-Maxwell-dilaton-axion (EMDA) theory). These correspond to null geodesics of the target space of the sigma-model $G/H=Sp(4,\mathbb{R})/GL(2,\mathbb{R})$ obtained by compactification of four-dimensional Euclidean EMDA on a circle. They satisfy a no-force condition in terms of the asymptotic charges and part of them (corresponding to nilpotent orbits of the $Sp(4,\mathbb{R})$ U-duality) are presumably supersymmetric. The space of finite action solutions is found to be unexpectedly large and includes, besides the Euclidean versions of known Lorentzian solutions, a number of new asymptotically locally flat (ALF) instantons endowed with electric, magnetic, dilaton and axion charges. We also describe new classes of charged asymptotically locally Euclidean (ALE) instantons as well as some exceptional solutions. Our classification scheme is based on the algebraic classification of matrix generators according to their rank, according to the nature of the charge vectors and according to the number of independent harmonic functions with unequal charges. Besides the nilpotent orbits of $G$, we find solutions which satisfy the asymptotic no-force condition, but are not supersymmetric. The renormalized on-shell action for instantons is calculated using the method of matched background subtraction.

A holographic description of extremal black holes

We show that the extremal Einstein–Maxwell–Dilaton–Axion (EMDA) black hole and the extremal Kaluza–Klein black hole have a hidden conformal symmetry. In this regard, we consider the wave equations of a massless scalar field propagating in EMDA and Kaluza–Klein spacetimes and find in the ‘near region', the wave equations in the extremal limit can be written in terms of SL(2, R) Casimir invariants. Moreover, we obtain the microscopic entropy of the extremal EMDA black hole and extremal Kaluza–Klein black hole and find that the correlation function of a near-region scalar field matches the microscopic graybody factor of the dual 2D CFT.

Hidden conformal symmetry of extreme and non-extreme Einstein-Maxwell-dilaton-axion black holes

The hidden conformal symmetry of extreme and non-extreme Einstein-Maxwell-Dilaton-Axion (EMDA) black holes is addressed in this paper. For the non-extreme one, employing the wave equation of massless scalars, the conformal symmetry with left temperature $ {T_L} = \frac{M}{{2\pi a}} $ and right temperature $ {T_R} = \frac{{\sqrt {{{M^2} - {a^2}}} }}{{2\pi a}} $ in the near region is found. The conformal symmetry is spontaneously broken due to the periodicity of the azimuthal angle. The microscopic entropy is derived by the Cardy formula and is fully in consistence with the Bekenstein-Hawking area-entropy law. The absorption cross section in the near region is calculated and exactly equals that in a 2D CFT. For the extreme case, by redefining the conformal coordinates, the duality between the solution space and CFT is studied. The microscopic entropy is found to exactly agree with the area-entropy law.

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.