Braneworld Black Hole Research Articles

Strong lensing as a probe of braneworld

For the first time, we use the Event Horizon Telescope (EHT) data to constrain the parameters of braneworld black holes which constrain ϵ = 0.0285+0.0888+0.1456 -0.0895-0.1475 for the anisotropic black hole and q = -0.0305+0.1034+0.1953 -0.0895-0.1470 for the tidal Reissner-Nordström (RN) black hole. Based on the fitted data and physical requirement, we calculate the photon deflection, the angular separation and time delay between different relativistic images of the anisotropic black hole and the tidal RN black hole in the ranges -0.1190 < ϵ < 0 and -0.1775 < q < 0. And furthermore, we study the quasinormal modes (QNMs) for the braneworld black holes. The results shed light on existence of extra dimension.

QPOs from charged particles around magnetized black holes in braneworlds

Quasiperiodic oscillations (QPOs) are a powerful tool for testing gravity theories, probing gravitational and electromagnetic field properties, and obtaining constraints on the black hole and field parameters. This work considers charged particle dynamics near uniformly magnetized black holes in braneworlds. First, we obtain the solution of the Maxwell equation for magnetic fields and calculate the radial and angular magnetic field components. We derive and analyze the effective potential of charged particles for circular orbits and investigate the energy and angular momentum for the circular orbits. We also analyze the combined effects of magnetic interaction and braneworlds on the charged particles’ innermost stable circular orbits (ISCOs). We calculate the angular momentum of charged particles in Keplerian orbits in the presence of an external magnetic field and braneworlds. Also, we investigate frequencies of the particle oscillations along vertical and angular directions. We applied our studies on particle oscillations to the QPO studies in the relativistic precession model. Finally, we obtain constraints on magnetic interaction and braneworld parameters together with the black hole mass and QPO orbits using Monte Carlo Markov Chain (MCMC) simulation in the four-dimensional parameter space for the QPOs observed in the microquasars XTE J1550-564, GRO J1655-40 & GRS 1915-105, and at the center of galaxies M82 and Milky Way.

Observable strong field effects of extra spacetime dimension in the braneworld black hole

Inspired by the string theory, the braneworld picture introduces extra dimensions beyond the four that may have observable non-trivial effects in short distance (strong field) gravity experiments. A case in point is the Randall–Sundrum braneworld picture that projects the 5d bulk Weyl tensor onto the 3d brane providing a stress tensor in the effective Einstein field equations on the brane. Dadhich, Maartens, Papadopoulos and Rezania (DMPR) derived an exact braneworld black hole solution of the brane vacuum field equations. The solution formally resembles that of Reissner–Nordström but is physically different from it since the ”tidal charge” Υ in the solution is not the electric charge but an imprint from the fifth dimension allowing both signs in the power law modification ±Υ2r2 to the Schwarzschild metric Υ=0. The corresponding black holes are designated as DMPR±. We study here the effect of Υ on strong field lensing observables and compare in the eikonal limit the ring down quasinormal mode (QNM) frequencies of DMPR− with those of DMPR＋ , the two variants of tidal charge modified Schwarzschild black hole (Υ=0). It turns out that the tidal charge can significantly modify the Schwarzschild lensing observables and QNM frequencies. In particular, we find that the Pretorius–Khurana critical exponent γ of circular null orbits in the DMPR− black hole has a lower value than that for the Schwarzschild black hole, which indicates a stronger Lyapunov instability suggesting that the accretion disks of DMPR− black holes would appear brighter. The case of the SgrA* black hole is considered for a possible constraint on Υ from the EHT observation of its shadow size.

Possible signatures of higher dimension in thin accretion disk around brane world black hole

We probe deeply into the characteristics of thin accretion disk surrounding black hole within the brane world paradigm. We investigate how model parameters affect the physical properties of the disk. Our findings indicate that as the tidal charge parameter inherited from the higher dimension increases, the energy flux, the radiation temperature, the spectral cutoff frequency, the spectral luminosity, and the conversion efficiency of the disk all increase, but the radius of the innermost stable circular orbit decreases. Compared to cases of the Kerr and Schwarzschild black holes, the disk is hotter and more luminous for positive tidal charge parameter, while it is cooler and less luminous for negative tidal charge parameter, which suggests the potential for probing possible signatures of higher dimension.

Telling late-time tails for a massive scalar field in the background of brane-localized black holes

We examine perturbations of a massive scalar field around spherically symmetric, brane-localized black holes. Although the ringdown and asymptotic tails of various brane-world black holes have been extensively studied, there has been no analysis of the massive late-time tails for the simplest Schwarzschild-like, brane-localized black hole to date. We demonstrate that after the ringdown phase, two stages of oscillatory tails emerge —intermediate and asymptotic. The asymptotic decay law is distinct from those associated with Schwarzschild or Reissner-Nordström solutions. Specifically, during intermediate times, the signal decays as , while the asymptotic decay law is .

Braneworld black holes with ModMax electrodynamics on the brane

In this study, we investigate ModMax electrodynamics localized within the Randall–Sundrum II and Dvali–Gabadadze–Porrati branes, deriving corresponding 3-brane spacetime solutions that conform to the effective Einstein equations in each specific scenario. We construct solutions for charged black holes within the effective Einstein equation framework in both braneworld scenarios. The examination explores the trajectories of charged objects in this spacetime, underscoring the significance of the nonlinear parameter. Our analysis uncovers the fact that, similar to the prior ModMax black hole investigation, the nonlinear parameter plays a pivotal role in suppressing the effective charge of the black hole, due to its definite positive value.

Horizon brightened accelerated radiation in the background of braneworld black holes

Horizon brightened accelerated radiation in the background of braneworld black holes

On the Kalb–Ramond modified Lorentz violating hairy black holes and Thorne’s hoop conjecture

Recently, a class of static spherically symmetric power law corrected Lorentz violating (LV) Schwarzschild black holes in the Kalb–Ramond model have been derived and studied in the specific range of LV parameters (0<lambda le 2,Upsilon ge 0) that correspond to energy condition preserving (rho >0) source. On the other hand, there exist well known black holes that do not preserve the energy conditions. In this paper, we shall therefore relax energy conditions and numerically explore the horizon patterns of the enlarged class of LSMA black holes. Four generic types of LV corrected black holes emerge, which interestingly include the analogue of the braneworld black hole (rho <0) lending to Upsilon a new interpretation of “tidal charge” known as an imprint from the 5d bulk in the Randall–Sundrum scenario. We shall then show that Thorne’s hoop conjecture, mathcal {H} le 1, where mathcal {H} is the Hod function, consistently holds for three types and their generalizations. However, intriguingly, it turns out that, for the remaining type (viz., Schwarzschild–de Sitter and its generalizations), the hoop conjecture does not hold. It is also shown that braneworld tidal charge black holes increases the LV correction to planetary perihelion advance in contrast to the decrease due to ordinary black holes thereby providing a qualitative distinction between them.

Transition from inspiral to plunge for braneworld EMRI

In the present article, we discuss the late inspiral and then the transition regime to the plunge phase of a secondary, less massive compact object into a more massive braneworld black hole, in the context of an extreme-mass-ratio inspiral. We obtain the approximate expressions for fluxes due to slowly evolving constants of motion, such as the energy and the angular momentum, in the presence of the tidal charge inherited from the higher spacetime dimensions for an extreme-mass-ratio system. These expressions for fluxes are further used to introduce dissipative effects while modelling the inspiral to the plunge phase through the transition regime. Within our setup, we provide a qualitative understanding of how the additional tidal charge present in the braneworld scenario may affect the timescale of the late inspiral to the plunge, in particular, by enhancing the time scale of the transition regime. Finally, we provide an estimate for the tidal charge from the higher dimensions, using the observable aspects of the transition regime from the late inspiral to the plunge by the gravitational wave detectors.

Maximal forces and thermodynamic quantities of specific black holes in modified theories of gravity

In this work, we explore the maximum force conjecture and thermal fluctuations for different black holes such as the brane-world black hole, de Rham-Gabadadze-Tolley black hole, Black-Bounce Reisner-Nordström black hole, and renormalization group improved Schwarzchild black hole. Thermodynamical parameters for these black holes are reviewed, including temperature, pressure, entropy, specific heat capacity at constant pressure and volume, the ratio of these heat capacities, Gibbs free energy, as well as Helmholtz free energy. In order to examine the stability conditions of the mentioned black holes, exponential corrected entropy is employed. The global and local stability of these black holes in a grand canonical and canonical ensemble is explored. Additionally, we compare the stability of the aforementioned black holes to inferred that which one is consistent.

Gravitational wave from extreme mass-ratio inspirals as a probe of extra dimensions

The field of gravitational waves is rapidly progressing due to the noticeable advancements in the sensitivity of gravitational-wave detectors that has enabled the detection prospects of binary black hole mergers. Extreme mass-ratio inspiral (EMRI) is one of the most compelling and captivating binary systems in this direction, with the detection possibility by the future space-based gravitational wave detector. In this article, we consider an EMRI system where the primary or the central object is a spherically symmetric static braneworld black hole that carries a tidal charge Q. We estimate the effect of the tidal charge on total gravitational wave flux and orbital phase due to a non-spinning secondary inspiralling the primary. We further highlight the observational implications of the tidal charge in EMRI waveforms. We show that LISA (Laser Interferometer Space Antenna) observations can put a much stronger constraint on this parameter than black hole shadow and ground-based gravitational wave observations, which can potentially probe the existence of extra dimensions.

Collisional Penrose process of braneworld black hole with spinning particles

The Penrose process of an extremal braneworld black hole is studied. We analyze the Penrose process by two massive spinning particles colliding near the horizon. By calculating the maximum energy extraction efficiency of this process, it turns out that the maximal efficiency increases as the tidal charge parameter d of the braneworld blackhole decreases. Interestingly, for the negative value of d, the efficiency can be even larger than the Kerr case.

Shadow of topologically charged rotating braneworld black hole

In this paper, we investigate the optical properties by a charged rotating braneworld black hole, in the Randall–Sundrum scenario. We study the horizon, the photon region, the shadow of the black hole and other observables. The results show that in addition to the black hole spin parameter [Formula: see text], the other two parameters, tidal charge [Formula: see text] and electric charge [Formula: see text], are found to affect the horizon, the photon region and the black hole shadow. We also have researched different observables and found that with the increase of the three parameters, the area and perimeter of the black hole shadow decrease, while the deformation of the shadow intensifies. Finally, through the observations of the oblateness [Formula: see text], the circularity deviation [Formula: see text] and the angular diameter [Formula: see text] and the latest M87[Formula: see text] and SgrA[Formula: see text] black hole shadows, the three parameters are analyzed to turn out that those observations give different constraints due to the three parameters.

Implications of the quantum nature of the black hole horizon on the gravitational-wave ringdown

Motivated by capturing putative quantum effects at the horizon scale, we model the black hole horizon as a membrane with fluctuations following a Gaussian profile. By extending the membrane paradigm at the semiclassical level, we show that the quantum nature of the black hole horizon implies partially reflective boundary conditions and a frequency-dependent reflectivity. This generically results into a modified quasi-normal mode spectrum and the existence of echoes in the postmerger signal. On a similar note, we derive the horizon boundary condition for a braneworld black hole that could originate from quantum corrections on the brane. This scenario also leads to a modified gravitational-wave ringdown. We discuss general implications of these findings for scenarios predicting quantum corrections at the horizon scale.

Chaos in a Magnetized Brane-World Spacetime Using Explicit Symplectic Integrators

A brane-world metric with an external magnetic field is a modified theory of gravity. It is suitable for the description of compact sources on the brane such as stars and black holes. We design a class of explicit symplectic integrators for this spacetime and use one of the integrators to investigate how variations of the parameters affect the motion of test particles. When the magnetic field does not vanish, the integrability of the system is destroyed. Thus, the onset of chaos can be allowed under some circumstances. Chaos easily occurs when the electromagnetic parameter becomes large enough. Dark matter acts as a gravitational force, so that chaotic motion can become more obvious as dark matter increases. The gravity of the black hole is weakened with an increasing positive cosmological parameter; therefore, the extent of chaos can be also strengthened. The proposed symplectic integrator is applied to a ray-tracing method and the study of such chaotic dynamics will be a possible reference for future studies of brane-world black hole shadows with chaotic patterns of self-similar fractal structures based on the Event Horizon Telescope data for M87* and Sagittarius A*.

Effects of dark matter on shadows and rings of Brane-World black holes illuminated by various accretions

Effects of dark matter on shadows and rings of Brane-World black holes illuminated by various accretions

Geodesics and optical properties of a rotating black hole in Randall–Sundrum brane with a cosmological constant

The presence of tidal charge and cosmological constant has considerable consequences on the spacetime geometry and its study is much more important from the observational point of view. Henceforth, we investigate their effects on particle dynamics and the shadow cast by a Randall–Sundrum braneworld black hole with a cosmological constant. On studying the circular geodesics of timelike particles, we have acquired the expressions of energy, angular momentum, effective potential and the innermost stable circular orbits on the equatorial plane. We noted that the negative values of tidal charge and cosmological constant decrease the energy of particles. In addition, the negative value of the cosmological constant leads us to stable circular orbits, whereas its positive value destabilizes the circular orbits. Our exploration shows that the cosmological constant diminishes the radius of the black hole shadow. In response to the dragging effect, black hole rotation elongates its shadow towards the rotational axis. Besides, black hole spin and positive charge distort shadow and its distortion becomes maximum as far as the black hole rotates faster. We also discussed the energy emission rate by considering different cases and compared our result with the standard Kerr black hole.

Effects of tidal charge on magnetic reconnection and energy extraction from spinning braneworld black hole

Recent study shows that the magnetic reconnection can serve as an efficient mechanism to extract energy from rapidly spinning black holes. In this paper, we consider the effects of the tidal charge on the energy extraction via the magnetic reconnection in the backgrounds of a spinning braneworld black hole. With the increase of the tidal charge, we find that both the energies of the accelerated plasma and decelerated plasma decrease for the observer located at infinity. To achieve the purpose extracting the net energy from the black hole, the decelerated plasma should take negative energy. Then we observe that the power of the energy extraction via the magnetic reconnection grows with the tidal charge. Meanwhile, the efficiency also increases with the tidal charge indicating that the spinning braneworld black hole with positive tidal charge is more efficient than the Kerr black hole. Compared with the Blandford-Znajek mechanism, the magnetic reconnection process shall have a higher power for positive tidal charge. These results indicate that the tidal charge has a significant effect on the energy extraction via the magnetic reconnection process.

Physical properties of brane-world black hole solutions via a confining potential

In this paper, we consider two brane-world black holes whose solutions are obtained via a confining potential and study their thermodynamical properties. The modified entropies by taking account of the generalized uncertainty principle (GUP) are obtained. We also determine the scalar effective potentials in order to compute the greybody factors of zero-spin particles (bosons) for both geometries. Finally, using the sixth-order WKB approach, quasi-normal modes (QNMs), which are also known as black hole fingerprints, are derived concerning the brane-world black hole parameters. The results obtained are graphically depicted, tabulated, and interpreted.

Constraining extra dimensions using observations of black hole quasi-normal modes

The presence of extra dimensions generically modify the spacetime geometry of a rotating black hole, by adding an additional hair, besides the mass M and the angular momentum J, known as the ‘tidal charge’ parameter, beta . In a braneworld scenario with one extra spatial dimension, the extra dimension is expected to manifest itself through – (a) negative values of beta , and (b) modified gravitational perturbations. This in turn would affect the quasi-normal modes of rotating black holes. We numerically solve the perturbed gravitational field equations using the continued fractions method and determine the quasi-normal mode spectra for the braneworld black hole. We find that increasingly negative values of beta correspond to a diminishing imaginary part of the quasi-normal mode, or equivalently, an increasing damping time. Using the publicly available data of the properties of the remnant black hole in the gravitational wave signal GW150914, we check for consistency between the predicted values (for a given beta ) of the frequency and damping time of the least-damped ell =2,m=2 quasi-normal mode and measurements of these quantities using other independent techniques. We find that it is highly unlikely for the tidal charge, beta lesssim -0.05, providing a conservative limit on the tidal charge parameter. Implications and future directions are discussed.