We investigate the strong gravitational lensing in a Kaluza-Klein black hole with squashed horizons. We find the size of the extra dimension imprints in the radius of the photon sphere, the deflection angle, the angular position and magnification of
the relativistic images. 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 coefficients and observables for gravitational lensing in the strong field limit.
We study the effects of the Born-Infeld electrodynamics on the holographic superconductors in the background of a Schwarzschild AdS black hole spacetime. We find that the presence of Born-Infeld scale parameter decreases the critical temperature and
the ratio of the gap frequency in conductivity to the critical temperature for the condensates. Our results means that it is harder for the scalar condensation to form in the Born-Infeld electrodynamics.
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 the negative kinetic energy terms modifies the standard results in the greybody factor, super-r
adiance and Hawking radiation. Comparing with the usual scalar particle, the phantom scalar emission is enhanced in the black hole spacetime.
We study holographic superconductors in the Schwarzschild-AdS black hole with a global monopole through a charged complex scalar field. We calculate the condensates of the charged operators in the dual conformal field theories (CFTs) and discuss the
effects of the global monopole on the condensation formation. Moreover, we compute the electric conductive using the probe approximation and find that the properties of the conductive are quite similar to those in the Schwarzschild-AdS black hole. These results can help us know more about holographic superconductors in the asymptotic AdS black holes.
We propose two improved parameterized form for the growth index of the linear matter perturbations: (I) $gamma(z)=gamma_0+(gamma_{infty}-gamma_0){zover z+1}$ and (II) $gamma(z)=gamma_0+gamma_1 frac{z}{z+1}+(gamma_{infty}-gamma_1-gamma_0)(frac{z}{z+1}
)^{alpha}$. With these forms of $gamma(z)$, we analyze the accuracy of the approximation the growth factor $f$ by $Omega^{gamma(z)}_m$ for both the $omega$CDM model and the DGP model. For the first improved parameterized form, we find that the approximation accuracy is enhanced at the high redshifts for both kinds of models, but it is not at the low redshifts. For the second improved parameterized form, it is found that $Omega^{gamma(z)}_m$ approximates the growth factor $f$ very well for all redshifts. For chosen $alpha$, the relative error is below 0.003% for the $Lambda$CDM model and 0.028% for the DGP model when $Omega_{m}=0.27$. Thus, the second improved parameterized form of $gamma(z)$ should be useful for the high precision constraint on the growth index of different models with the observational data. Moreover, we also show that $alpha$ depends on the equation of state $omega$ and the fractional energy density of matter $Omega_{m0}$, which may help us learn more information about dark energy and DGP models.
Using Leavers continue fraction and time domain method, we study the wave dynamics of phantom scalar perturbation in a Schwarzschild black string spacetime. We find that the quasinormal modes contain the imprint from the wavenumber $k$ of the fifth d
imension. The late-time behaviors are dominated by the difference between the wavenumber $k$ and the mass $mu$ of the phantom scalar perturbation. For $k<mu$, the phantom scalar perturbation in the late-time evolution grows with an exponential rate as in the four-dimensional Schwarzschild black hole spacetime. While, for $k=mu$, the late-time behavior has the same form as that of the massless scalar field perturbation in the background of a black hole. Furthermore, for $k>mu$, the late-time evolution of phantom scalar perturbation is dominated by a decaying tail with an oscillation which is consistent with that of the usual massive scalar field. Thus, the Schwarzschild black string is unstable only against the phantom scalar perturbations which satisfy the wavelength $lambda>2pi/mu$. These information can help us know more about the wave dynamics of phantom scalar perturbation and the properties of black string.
Using Leavers continue fraction and time domain method, we investigate the wave dynamics of phantom scalar perturbation in the background of Schwarzschild black hole. We find that the presence of the negative kinetic energy terms modifies the standar
d results in quasinormal spectrums and late-time behaviors of the scalar perturbations. The phantom scalar perturbation in the late-time evolution will grow with an exponential rate.
We investigate the background dynamics when dark energy is coupled to dark matter in the universe described by Einstein cosmology and Loop Quantum Cosmology. We introduce a new general form of dark sector coupling, which presents us a more complicate
d dynamical phase space. Differences in the phase space in obtaining the accelerated scaling attractor in Einstein cosmology and Loop Quantum Cosmology are disclosed.
We study the absorption probability and Hawking radiation of the scalar field in the rotating G{o}del black hole in minimal five-dimensional gauged supergravity. We find that G{o}del parameter $j$ imprints in the greybody factor and Hawking radiation
. It plays a different role from the angular momentum of the black hole in the Hawking radiation and super-radiance. These information can help us know more about rotating G{o}del black holes in minimal five-dimensional gauged supergravity.
We present a solution of Einstein equations with quintessential matter surrounding a $d$-dimensional black hole, whose asymptotic structures are determined by the state of the quintessential matter. We examine the thermodynamics of this black hole an
d find that the mass of the black hole depends on the equation of state of the quintessence, while the first law is universal. Investigating the Hawking radiation in this black hole background, we observe that the Hawking radiation dominates on the brane in the low-energy regime. For different asymptotic structures caused by the equation of state of the quintessential matter surrounding the black hole, we learn that the influences by the state parameter of the quintessence on Hawking radiation are different.
