Jiliang Jing

Quasinormal modes of a black hole surrounded by quintessence

Using the third-order WKB approximation, we evaluate the quasinormal frequencies of massless scalar field perturbation around a black hole which is surrounded by static and spherically symmetric quintessence. Our result shows that due to the presence of quintessence, the scalar field damps more rapidly. Moreover, we also note that the quintessential state parameter (the ratio of pressure pq to the energy density ρq) plays an important role for the quasinormal frequencies. As the state parameter increases, so does the real part and the absolute value of the imaginary part decreases. This means that the scalar field decays more slowly in the larger quintessence case.

Asymptotic quasinormal modes of a coupled scalar field in the Garfinkle-Horowitz-Strominger dilaton spacetime

The analytic forms of the asymptotic quasinormal frequencies of a coupled scalar field in the Garfinkle-Horowitz-Strominger dilaton spacetime are investigated by using the monodromy technique proposed by Motl and Neitzke. It is found that the asymptotic quasinormal frequencies depend not only on the structure parameters of the background spacetime, but also on the coupling between the scalar fields and gravitational field. Moreover, our results show that only in the minimally coupled case, i.e., ξ tends to zero, the real parts of the asymptotic quasinormal frequencies agree with Hods conjecture, T H In 3.

What kind of coordinate can keep the Hawking temperature invariant for the static spherically symmetric black hole

By studying the Hawking radiation of the most general static spherically symmetric black hole arising from scalar and Dirac particles tunnelling, we find the Hawking temperature is invariant in the general coordinate representation (\ref{arbitrary1}), which satisfies two conditions: a) its radial coordinate transformation is regular at the event horizon; and b) there is a time-like Killing vector.

Geodetic precession and strong gravitational lensing in dynamical Chern–Simons-modified gravity

We have investigated the geodetic precession and the strong gravitational lensing in the slowly rotating black hole in the dynamical Chern–Simons-modified gravity theory. We present the formulas of the orbital period T and the geodetic precession angle ΔΘ for the timelike particles in the circular orbits around the black hole, which shows that the change of the geodetic precession angle with the Chern–Simons coupling parameter ξ is converse to the change of the orbital period with ξ for fixed a. We also discuss the effects of the Chern–Simons coupling parameter on the strong gravitational lensing when the light rays pass close to the black hole and obtain that for the stronger Chern–Simons coupling the prograde photons may be captured more easily, and conversely, the retrograde photons are harder to capture in the slowly rotating black hole in the dynamical Chern–Simons-modified gravity. Supposing that the gravitational field of the supermassive central object of the Galaxy can be described by this metric, we estimated the numerical values of the main observables for gravitational lensing in the strong field limit.

Asymptotic quasinormal modes of a coupled scalar field in the Gibbons-Maeda dilaton spacetime

Adopting the monodromy technique devised by Motl and Neitzke, we investigate analytically the asymptotic quasinormal frequencies of a coupled scalar field in the Gibbons–Maeda dilaton spacetime. We find that it is described by , which depends on the structure parameters of the background spacetime and on the coupling between the scalar and gravitational fields. As the parameters ξ and βI tend to zero, the real parts of the asymptotic quasinormal frequencies become THln 3, which is consistent with Hods conjecture. When , the formula becomes that of the Reissner–Nordstrom spacetime.

A dark energy model interacting with dark matter and unparticle

We study dynamical behaviors of dark energy models interacting with dark matter and unparticle in the standard flat Friedmann–Robertson–Walker cosmology. We considered four different interacting models and examined the stability of the critical points. We find that there exist late-time scaling attractors corresponding to an accelerating universe, and the alleviation of the coincidence problem depends on the choice of parameters in the models.

Dirac quasinormal modes of the Garfinkle-Horowitz-Strominger dilaton black-hole spacetime

Adopting the P?schl?Teller potential approximation, the quasinormal frequencies of the massless Dirac fields are evaluated in the Garfinkle?Horowitz?Strominger dilaton black-hole spacetime. We find that the real parts of the quasinormal frequencies increase as the orbital angular momentum k or a increases, where a is a parameter related to the dilaton field. The magnitude of imaginary parts decreases with k for the fixed a and overtone number n, while for fixed k and n, it is not a monotonic function of a and has a maximum at a point near a = 1.4?1.6, where the waves decay most rapidly. Another interesting feature is that the imaginary parts tend to zero and the real parts to k/2 as a approaches 2. We also find that the variation of the imaginary parts with the real parts in the Garfinkle?Horowitz?Strominger dilaton hole spacetimes is nonlinear, which becomes more complex than that in the Reissner?Nordstr?m black-hole spacetime.

Phantom scalar emission in the Kerr black hole spacetime

We study the absorption probability and Hawking radiation spectra of a phantom scalar field in the Kerr black hole spacetime. We find that the presence of negative kinetic energy terms modifies the standard results in the graybody factor, super-radiance and Hawking radiation. Comparing with the usual scalar particle, the phantom scalar emission is enhanced in the black hole spacetime.

Gravitational field of a slowly rotating black hole with a phantom global monopole

We present a slowly rotating black hole solution with a phantom global monopole by solving Einsteins field equation and find that the presence of the global monopole changes the black hole structure. The metric coefficient gtϕ contains the hypergeometric function of the polar coordinate r, which is more complex than that in the usual slowly rotating black hole. The energy scale of symmetry breaking η affects the black hole horizon and the deficit solid angle. In particular, the solid angle is surplus rather than deficit for the black hole with the phantom global monopole. We also study the effects of the global monopole on the angular velocity of the horizon ΩH, Keplers third law, the innermost stable circular orbit and the radiative efficiency ϵ in the thin accretion disc model. Our results also show that for a phantom black hole, the radiative efficiency ϵ is positive only in the case η ⩽ ηc. The threshold value ηc increases with the rotation parameter a.

Energy of general four-dimensional stationary axisymmetric spacetime in the teleparallel geometry

A field equation with a cosmological constant term is derived and the energy of a general four-dimensional stationary axisymmetric spacetime is studied in the context of the Hamiltonian formulation of the teleparallel equivalent of general relativity (TEGR). We find that, by means of the integral form of the constraint equations of the formalism naturally without any restriction on the metric parameters, the energy for the asymptotically flat/de Sitter/anti-de Sitter stationary spacetimes in the Boyer?Lindquist coordinate can be expressed as . It is surprising to learn that the energy expression is only relevant to the metric components grr, g?? and g. As examples, by using this formula we calculate the energies of the Kerr?Newman (KN), Kerr?Newman anti-de Sitter (KN?AdS), Kaluza?Klein and Cveti??Youm spacetimes.