Dirac quasinormal modes of Born-Infeld black hole spacetimes

Quasinormal modes (QNMs) for massless and massive Dirac perturbations of Born-Infeld black holes (BHs) in higher dimensions are investigated. Solving the corresponding master equation in accordance with hypergeometric functions and the QNMs are evaluated. We discuss the relationships between QNM frequencies and spacetime dimensions. Meanwhile, we also discuss the stability of the Born-Infeld BH by calculating the temporal evolution of the perturbation field. Both the perturbation frequencies and the decay rate increase with increasing dimension of spacetime n. This shows that the Born-Infeld BHs become more and more unstable at higher dimensions. Furthermore, the traditional finite difference method is improved, so that it can be used to calculate the massive Dirac field. We also elucidate the dynamic evolution of Born-Infeld BHs in a massive Dirac field. Because the number of extra dimensions is related to the string scale, there is a relationship between the spacetime dimension n and the properties of Born-Infeld BHs that might be advantageous for the development of extra-dimensional brane worlds and string theory.     

Comparison of thermodynamic behaviors of two regular-AdS black holes

Considering the negative cosmological constant of an anti-de Sitter (AdS) background as a positive thermodynamic pressure in the extended phase space, we investigate the P−υ critical behavior and of the cooling–heating phase transition of the regular Hayward-AdS (HAdS) black hole (BH), and compare the difference of some thermodynamic processes in both the HAdS BH and the Bardeen-AdS (BAdS) BH. We found that the phase transition of the BAdS BH tends to be more the van der Waals (vdW) phase transition. For the cooling–heating phase transition, we obtained the inversion curves of the HAdS BH are always higher than the BAdS BH under the same pressure and magnetic charge. We also compare the smallest existence mass, the zero-temperature remnant, and the critical magnetic charge for these two BHs. The results suggested that the inner horizon and the outer horizon of the Hayward BH are easier to merge, and the singularity is easier to expose.     

Quantum effects on the black hole shadow and deflection angle in the presence of plasma

In this study, the optical properties of a renormalization group improved (RGI) Schwarzschild black hole (BH) are investigated in a plasma medium. Beginning with the equations of motion in a plasma medium, we aim to present the modifications in the shadow radius of the RGI BH. To this end, we compute the deflection angle of light in the weak gravity regime for uniform and non-uniform plasma media. Importantly, owing to the plasma media, we discover that the equations of motion for light obtained from the radiating and infalling/rest gas have to be modified. This, in turn, changes and modifies the expression for the intensity observed far away from the BH. Finally, we obtain the shadow images for the RGI BH for different plasma models. Although quantum effects change the background geometry, such effects are minimal, and practically detecting these effects using the current technology based on supermassive BH shadows is impossible. The parameter Ω encodes the quantum effects, and in principle, one expects such quantum effects to play significant roles only for very small BHs. However, the effects of plasma media can play an important role in the optical appearance of BHs, as they affect and modify the equations of motion.     

Prospects for detection of gravitational waves from intermediate-mass-ratio inspirals

We explore prospects for detecting gravitational waves from stellar-mass compact objects spiraling into intermediate mass black holes (BHs) M approximately 50M to 350M) with ground-based observatories. We estimate a rate for such intermediate-mass-ratio inspirals of 相似文献   

Regular phantom black holes

We study self-gravitating, static, spherically symmetric phantom scalar fields with arbitrary potentials (favored by cosmological observations) and single out 16 classes of possible regular configurations with flat, de Sitter, and anti-de Sitter asymptotics. Among them are traversable wormholes, bouncing Kantowski-Sachs (KS) cosmologies, and asymptotically flat black holes (BHs). A regular BH has a Schwarzschild-like causal structure, but the singularity is replaced by a de Sitter infinity, giving a hypothetic BH explorer a chance to survive. It also looks possible that our Universe has originated in a phantom-dominated collapse in another universe, with KS expansion and isotropization after crossing the horizon. Explicit examples of regular solutions are built and discussed. Possible generalizations include k-essence type scalar fields (with a potential) and scalar-tensor gravity.     

Observable signatures of a black hole ejected by gravitational-radiation recoil in a galaxy merger

According to recent simulations, the coalescence of two spinning black holes (BHs) could lead to a BH remnant with recoil speeds of up to thousands of km s(-1). Here we examine the circumstances resulting from a gas-rich galaxy merger under which the ejected BH would carry an accretion disk and be observable. As the initial BH binary emits gravitational radiation and its orbit tightens, a hole is opened in the disk which delays the consumption of gas prior to the eventual BH ejection. The punctured disk remains bound to the ejected BH within the region where the gas orbital velocity is larger than the ejection speed. For a approximately 10(7) M[middle dot in circle] BH the ejected disk has a characteristic size of tens of thousands of Schwarzschild radii and an accretion lifetime of approximately 10(7) yr. During that time, the ejected BH could traverse a considerable distance and appear as an off-center quasar with a feedback trail along the path it left behind.     

Discovering new physics in the decays of black holes

If the scale of quantum gravity is near a TeV, the CERN Large Hadron Collider (LHC) will be producing one black hole (BH) about every second, thus qualifying as a BH factory. With the Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may produce new, undiscovered particles with masses approximately 100 GeV. The probability of producing a heavy particle in the decay depends on its mass only weakly, in contrast with the exponentially suppressed direct production. Furthermore, backgrounds in the BH sample can be made small. Using the Higgs boson as an example, we show that it may be found at the LHC on the first day of its operation, even with incomplete detectors.     

Current–voltage characteristics of Al/Rhodamine-101/n-GaAs structures in the wide temperature range

The forward bias current–voltage (I–V) characteristics of Al/Rhodamine-101/n-GaAs structure have been investigated in the temperature range of 80–350 K. It has been seen a decrease in ideality factor (n) and an increase in the zero-bias barrier height (BH) with an increase in temperature. It has been seen that such a behavior of the BH and n obey Gaussian distribution of the BHs due to the BH inhomogeneities at the metal/semiconductor (MS) interface. The very strong temperature dependence of ideality factor of the structure has shown that the current processes occurring in the organic layer at the MS interface would be a possible candidate such as trap-charge limited conduction in determining the current at the intermediate and high bias regimes. Furthermore, it has been show that the Rh101 can be used to vary effective BHs for the metal/GaAs Schottky diodes. As a result, it has been determined that the BH value for conventional Al/n-GaAs SBD is remarkably higher than our own values of 0.68 eV obtained for the Al/Rh101/n-GaAs at 290 K.     

Emergent horizon,Hawking radiation and chaos in the collapsed polymer model of a black hole

We have proposed that the interior of a macroscopic Schwarzschild black hole (BH) consists of highly excited, long, closed, interacting strings and, as such, can be modeled as a collapsed polymer. It was previously shown that the scaling relations of the collapsed‐polymer model agree with those of the BH. The current paper further substantiates this proposal with an investigation into some of its dynamical consequences. In particular, we show that the model predicts, without relying on gravitational effects, an emergent horizon. We further show that the horizon fluctuates quantum mechanically as it should and that the strength of the fluctuations is inversely proportional to the BH entropy. It is then demonstrated that the emission of Hawking radiation is realized microscopically by the quantum‐induced escape of small pieces of string, with the rate of escape and the energy per emitted piece both parametrically matching the Hawking temperature. We also show, using standard methods from statistical mechanics and chaos theory, how our model accounts for some other known properties of BHs. These include the accepted results for the scrambling time and the viscosity‐to‐entropy ratio, which in our model apply not only at the horizon but throughout the BH interior.     

Thermal consequences of a regular black hole with cosmological constant and Einstein–Aether black hole

We discuss the thermodynamics of regular black hole (RBH) with cosmological constant and Einstein–Aether black hole (BH) with coupling constant in the presence of thermal corrections. For these BHs, we develop various thermodynamical quantities such as entropy, pressure, specific heats, Gibbs free energy and Helmholtz free energy. Thermal stability is also being analyzed through γ factor, Gibbs free energy and Helmholtz free energy. It is found that RBH with cosmological constant and Einstein–Aether show stable behavior with the increase of the values of cosmological and coupling constants.     

Lectures on attractors and black holes

A basic survey on some aspects of four‐dimensional black holes (BHs) is given in these lectures. It covers thermodynamical properties as well as the Attractor Mechanism for extremal BHs in an environment of scalar field background. Some relevant formulæ for the critical points of the BH “effective potential” are discussed, and the simplest example uncovering the attractor behavior, the Maxwell‐Einstein‐dilaton supergravity, is analyzed in detail. Observations on similarities between BH entropy (as given by the Bekenstein‐Hawking entropy‐area formula) and multipartite entanglement of qubits in quantum information theory are reported, as well. Finally, among the latest developments, the moduli space of attractor points for 𝒩 ≥ 2 supergravities is also considered. Based on lectures given by S. Ferrara at the International School of Subnuclear Physics, 45th Course: Search for the “Totally Unexpected” in the LHC era, Erice, Italy, 29 August – 7 September 2007 (Directors: G. 't Hooft – A. Zichichi), and at the III Avogadro Meeting on Theoretical Physics, Alessandria, Italy, 19 – 21 December 2007.     

Weak deflection angle and shadow cast by the charged-Kiselev black hole with cloud of strings in plasma

In this study, the gravitational deflection angle of photons in the weak field limit (or the weak deflection angle) and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole (BH) in the string cloud background are investigated. The influences of the BH charge Q, quintessence parameter γ, and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem, in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the charged-Kiselev BH in string clouds. Moreover, we study the effects of plasma (uniform and non-uniform) on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings. In the presence of a uniform/nonuniform plasma medium, an increase in the string cloud parameter a increases the deflection angle α. In contrast, a decrease in the BH charge Q decreases the deflection angle. Further, we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH. We notice that, with an increase in the values of the parameters γ and a, the size of the BH shadow increases, and therefore, the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases. Thus, the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH. Moreover, we use the data released by the Event Horizon Telescope (EHT) collaboration, for the supermassive BHs M87* and Sgr A*, to obtain constraints on the values of the parameters γ and a.     

Testing the quantum effects near the event horizon with respect to the black hole shadow

In recent years, the study of quantum effects near the event horizon of a black hole (BH) has attracted extensive attention. It has become one of the important methods to explore BH quantum properties using the related properties of a quantum deformed BH. In this work, we study the effect of a quantum deformed BH on the BH shadow in two-dimensional Dilaton gravity. In this model, quantum effects are reflected by the quantum correction parameter m. By calculation, we find that: (1) the shape of the shadow boundary of a rotating BH is determined by the BH spin a, the quantum correction parameter m, and the BH type parameter n; (2) when the spin \begin{document}$ a=0 $\end{document}, the shape of the BH shadow is a perfect circle; when \begin{document}$ a\neq 0 $\end{document}, the shape is distorted; if the quantum correction parameter \begin{document}$ m=0 $\end{document}, their shapes reduce to the cases of a Schwarzschild BH and Kerr BH, respectively; (3) the degree of distortion of the BH shadow is different for various quantum correction parameters m; with an increase in the parameter m, the boundary of the BH shadow expands; (4) the size of the BH shadow varies greatly with respect to various quantum deformed BHs (n), and the change in BH shadow shape caused by parameter n is similar to that caused by parameter m, which indicates that there is a "degenerate phenomenon" between the two parameters. Because the value of m in actual physics should be very small, the current observations of the event horizon telescope (EHT) cannot distinguish quantum effects from the BH shadow. In future BH shadow measurements, it will be possible to distinguish quantum deformed BHs, which will help to better understand the quantum effects of BHs.     

The barrier-height inhomogeneity in identically prepared Ni/n-type 6H-SiC Schottky diodes

The effective barrier heights and ideality factors of identically fabricated Ni/n-type 6 H-SiC Schottky diodes (23 dots) have been calculated from their experimental forward bias current–voltage (I–V) and reverse bias capacitance–voltage (C–V) characteristics. A statistical study related to the experimental barrier heights (BHs) and ideality factors of the diodes has been made. The effective Schottky barrier heights (SBHs) and ideality factors obtained from the I–V and C–V characteristics have differed from diode to diode. The BHs obtained from the I–V characteristics varied from 0.85 to 1.03 eV, the ideality factors varied from 1.13 to 1.40 and the BHs from C^-2–V characteristics varied from 1.10 to 1.70 eV. The experimental BH and ideality factor distributions obtained from the I–V characteristics are fitted by a Gaussian function, and their mean values are found to be 0.92±0.04 eV and 1.29±0.08 eV, respectively. The lateral homogeneous SBH value of 1.16 eV for the Ni/n-type 6H-SiC diodes has been calculated from a linear extrapolation of the effective barrier heights to n_if=1.03. PACS 79.40.+z; 73.40.Sx; 73.30.+y; 71.20.Nr     

Quantum information paradox: Real or fictitious?

One of the outstanding puzzles of theoretical physics is whether quantum information indeed gets lost in the case of black hole (BH) evaporation or accretion. Let us recall that quantum mechanics (QM) demands an upper limit on the acceleration of a test particle. On the other hand, it is pointed out here that, if a Schwarzschild BH exists, the acceleration of the test particle would blow up at the event horizon in violation of QM. Thus the concept of an exact BH is in contradiction with QM and quantum gravity (QG). It is also reminded that the mass of a BH actually appears as an integration constant of Einstein equations. And it has been shown that the value of this integration constant is actually zero! Thus even classically, there cannot be finite mass BHs though zero mass BH is allowed. It has been further shown that during continued gravitational collapse, radiation emanating from the contracting object gets trapped within it by the runaway gravitational field. As a consequence, the contracting body attains a quasi-static state where outward trapped radiation pressure gets balanced by inward gravitational pull and the ideal classical BH state is never formed in a finite proper time. In other words, continued gravitational collapse results in an ‘eternally collapsing object’ which is a ball of hot plasma and which is asymptotically approaching the true BH state with M = 0 after radiating away its entire mass energy. And if we include QM, this contraction must halt at a radius suggested by the highest QM acceleration. In any case no event horizon (EH) is ever formed and in reality, there is no quantum information paradox.     

Dirac Quasinormal Modes of Static f(R) de Sitter Black Holes

Quasinormal modes(QNMs) for Dirac perturbations of f(R) black holes(BHs) are described in this paper,involving two types of f(R) solution: f(R)(Schwarzschild) BHs and f(R)(Maxwell) BHs. With the finite difference method, the stability of the f(R) black holes(BHs) is analysed and the threshold range of f(R)(Schwarzschild) BHs and f(R)(Maxwell) BHs is defined respectively. The results show that due to the presence of the correction factor R0, the damping rate of Dirac field decreases. Meanwhile, the influence of angular quantum number values |k| on the f(R) BHs is investigated. The results indicate that the QNMs oscillation becomes tenser and damping speed slowly decreases with|k| increasing. Furthermore, under the Dirac perturbation, the stability of f(R) solutions can be reflected in the manner of Dirac QNMs. The relationships between the QNMs and the parameters(|k|, charge Q and mass m) are discussed in massless, and massive cases, by contrast to the classical BHs.     

Temperature Profile of Black Hole Accretion Disc with Magnetic Coupling

Two new mapping relations between the angular coordinate on the black hole (BH) horizon and radialcoordinate on the disc are given according to the requirement of general relativity and Maxwell‘s equations, and theeffects of magnetic coupling (MC) on temperature of accretion disc are investigated by comparing with pure accretion.It is shown that the MC effects on the temperature profile are related intimately to the BH spin, and the influenceon the peak value of disc temperature based on the modified mapping relations is not as great as that based on thelinear mapping.The peak value and the corresponding radius of peak value ring of disc temperature do not increasemonotonically as the increasing spin of BH, each containing a maximum for the fast-spinning BH. The value ranges ofthe bolometric luminosity and color temperature of the disc are both extended by the MC effects.     

Dark matter in galaxies and the growth of giant black holes

The relationship of dark matter to giant black holes (BHs) in galactic nuclei is investigated. The simultaneous evolution of dark and baryonic matter under the effect of an averaged self-consistent gravitational field is considered. The distribution of dark matter is shown to remain spherically symmetric even if there is an appreciable asymmetry in the distribution of baryonic matter in the galaxy. A kinetic equation that describes the evolution of the distribution function for dark matter with gravitational scattering by stars is derived. A significant flux of dark matter on a seed BHe at the galactic center is shown to arise under these conditions. The law of growth of the seed BH via the absorption of dark matter has been established. The seed BH is shown to grow significantly, up to 10⁷–10⁸ M⊙, in the lifetime of the galaxy. Observational data are briefly analyzed, and the presented theory has been found to be in reasonable agreement with experimental data.

     

Magnetized hypermassive neutron-star collapse: a central engine for short gamma-ray bursts

A hypermassive neutron star (HMNS) is a possible transient formed after the merger of a neutron-star binary. In the latest axisymmetric magnetohydrodynamic simulations in full general relativity, we find that a magnetized HMNS undergoes "delayed" collapse to a rotating black hole (BH) as a result of angular momentum transport via magnetic braking and the magnetorotational instability. The outcome is a BH surrounded by a massive, hot torus with a collimated magnetic field. The torus accretes onto the BH at a quasisteady accretion rate [FORMULA: SEE TEXT]; the lifetime of the torus is approximately 10 ms. The torus has a temperature [FORMULA: SEE TEXT], leading to copious ([FORMULA: SEE TEXT]) thermal radiation that could trigger a fireball. Therefore, the collapse of a HMNS is a promising scenario for generating short-duration gamma-ray bursts and an accompanying burst of gravitational waves and neutrinos.