We investigate the propagation and evolution for a massless scalar field in the background of $lambda=1/2$ Hov{r}ava-Lifshitz black hole with the condition of detailed balance. We fortunately obtain an exact solution for the Klein-Gordon equation. Th
en, we find an analytical expression for the greybody factor which is valid for any frequency; and also exactly show that the perturbation decays without any oscillation. All of these can help us to understand more about the Hov{r}ava-Lifshitz gravity.
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 study the dynamical evolution of a massless scalar perturbation in the Hov{r}ava-Lifshitz black-hole spacetimes with the coupling constants $lambda={1/3}$, $lambda={1/2}$ and $lambda=3$, respectively. Our calculation shows that, for the three case
s, the scalar perturbations decay without any oscillation in which the decay rate imprints the parameter of the Hov{r}ava-Lifshitz black hole. The results are quite different from those in the Schwarzschild AdS black hole and can help us understand more about the Hov{r}ava-Lifshitz gravity.
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.
The entanglement of the coupled massive scalar field in the spacetime of a Garfinkle-Horowitz-Strominger(GHS) dilaton black hole has been investigated. It is found that the entanglement does not depend on the mass of the particle and the coupling bet
ween the scalar field and the gravitational field, but it decreases as the dilaton parameter $D$ increases. It is interesting to note that in the limit of $Dto M$, corresponding to the case of an extreme black hole, the state has no longer distillable entanglement for any state parameter $alpha$, but the mutual information equals to a nonvanishing minimum value, which indicates that the total correlations consist of classical correlations plus bound entanglement in this limit.
We study the quasinormal modes of scalar perturbation in the background of five-dimensional charged Kaluza-Klein black holes with squashed horizons immersed in the G{o}del universe. Besides the influence due to the compactness of the extra dimension,
we disclose the cosmological rotational effect in the wave dynamics. The wave behavior affected by the G{o}del parameter provides an interesting insight into the G{o}del universe.
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.
