arXiv subjects

Songbai Chen

Publications and source records attributed to Songbai Chen.

At least 127 records · Page 7Linked to original sources

arXiv2010

Holographic superconductor models in the non-minimal derivative coupling theory

We study a general class of holographic superconductor models via the Stückelberg mechanism in the non-minimal derivative coupling theory in which the charged scalar field is kinetically coupling to Einstein's tensor. We explore the effects of the coupling parameter on the critical temperature, the order of phase transitions and the critical exponents near the second-order phase transition point. Moreover, we compute the electric conductive using the probe approximation and check the ratios $ω_g/T_c$ for the different coupling parameters.

gr-qc↗

arXiv2010

Second-order phase transition of Kehagias-Sfetsos black hole in deformed Hǒrava-Lifshitz gravity

We study the second-order phase transition (SOPT) for the spherically symmetric Kehagias-Sfetsos (KS) black hole in the deformed Hǒrava-Lifshitz gravity by applying the methods of equilibrium and non-equilibrium fluctuations. We find that, although the KS black hole has only one mass parameter as the usual Schwarzschild ones, the SOPT will take place if the mass of the KS black hole changes across the critical point $\frac{\sqrt{5+\sqrt{33}}(\sqrt{33}-1)} {16\sqrtω} $. The result show us that there is difference between the Hǒrava-Lifshitz gravity and the Einstein's gravity theory.

gr-qc↗

arXiv2010

Extension of non-minimal derivative coupling theory and Hawking radiation in black-hole spacetime

We study the greybody factor and Hawking radiation with a non-minimal derivative coupling between the scalar field and the curvature in the background of the slowly rotating Kerr-Newman black hole. Our results show that both the absorption probability and luminosity of Hawking radiation of the scalar field increase with the coupling. Moreover, we also find that for the weak coupling $η<η_c$, the absorption probability and luminosity of Hawking radiation decrease when the black hole's Hawking temperature decreases; while for stronger coupling $η>η_c$, the absorption probability and luminosity of Hawking radiation increase on the contrary when the black hole's Hawking temperature decreases. This feature is similar to the Hawking radiation in a $d$-dimensional static spherically-symmetric black hole surrounded by quintessence \cite{chensong}.

gr-qc↗

arXiv2010

Geodetic precession and strong gravitational lensing in the 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 is harder to be captured 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.

gr-qc↗

arXiv2010

Dynamical evolution of a scalar field coupling to Einstein's tensor in the Reissner-Nordström black hole spacetime

We study the dynamical evolution of a scalar field coupling to Einstein's tensor in the background of Reissner-Nordström black hole. Our results show that the the coupling constant $η$ imprints in the wave dynamics of a scalar perturbation. In the weak coupling, we find that with the increase of the coupling constant $η$ the real parts of the fundamental quasinormal frequencies decrease and the absolute values of imaginary parts increase for fixed charge $q$ and multipole number $l$. In the strong coupling, we find that for $l\neq0$ the instability occurs when $η$ is larger than a certain threshold value $η_c$ which deceases with the multipole number $l$ and charge $q$. However, for the lowest $l=0$, we find that there does not exist such a threshold value and the scalar field always decays for arbitrary coupling constant.

gr-qc↗

arXiv2010

Greybody factor for a scalar field coupling to Einstein's tensor

We study the greybody factor and Hawking radiation for a scalar field coupling to Einstein's tensor in the background of Reissner-Nordström black hole in the low-energy approximation. We find that the presence of the coupling terms modifies the standard results in the greybody factor and Hawking radiation. Our results show that both the absorption probability and Hawking radiation increase with the coupling constant. Moreover, we also find that for the stronger coupling, the charge of black hole enhances the absorption probability and Hawking radiation of the scalar field, which is different from those of ones without coupling to Einstein's tensor in the black hole spacetime.

gr-qc↗

arXiv2010

Analytical expressions for greybody factor and dynamic evolution for scalar field in Hořava-Lifshitz black hole

We investigate the propagation and evolution for a massless scalar field in the background of $λ=1/2$ Hořava-Lifshitz black hole with the condition of detailed balance. We fortunately obtain an exact solution for the Klein-Gordon equation. Then, 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 Hořava-Lifshitz gravity.

gr-qc↗

arXiv2010

Holographic superconductors in the AdS black hole spacetime with a global monopole

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.

gr-qc↗

arXiv2010

Holographic superconductors in the Born-Infeld electrodynamics

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.

gr-qc↗

arXiv2010

Strong gravitational lensing in a squashed Kaluza-Klein black hole spacetime

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.

gr-qc↗

arXiv2010

Holographic Superconductors in $z=3$ Hořava-Lifshitz gravity without condition of detailed balance

We study holographic superconductors in a Hořava-Lifshitz black hole without the condition of the detailed balance. We show that it is easier for the scalar hair to form as the parameter of the detailed balance becomes larger, but harder when the mass of the scalar field larger. We also find that the ratio of the gap frequency in conductivity to the critical temperature, $ω_{g}/T_c$, almost linear decreases with the increase of the balance constant. For $ε= 0$ the ratio reduces to Cai's result $ω_g/T_c\approx 13$ found in the Hořava-Lifshitz black hole with the condition of the detailed balance, while as $ε\rightarrow 1$ it tends to Horowitz-Roberts relation $ω_g/T_c\approx 8$ obtained in the AdS Schwarzschild black hole. Our result provides a bridge between the results for the Hǒrava-Lifshitz theory with the condition of the detailed balance and Einstein's gravity.

hep-th↗

arXiv2010

First laws of thermodynamics in IR Modified Hǒrava-Lifshitz gravity

We study the first law of thermodynamics in IR modified Hǒrava-Lifshitz spacetime. Based on the Bekenstein-Hawking entropy, we obtain the integral formula and the differential formula of the first law of thermodynamics for the Kehagias-Sfetsos black hole by treating $ω$ as a new state parameter and redefining a mass that is just equal to $M_{ADM}$ obtained by Myung\cite{YSM2} if we take $α=3π/8$.

gr-qc↗

arXiv2010

Quasinormal modes of a black hole in the deformed Hořava-Lifshitz gravity

We study the quasinormal modes of the massless scalar perturbation in the background of a deformed black hole in the Hořava-Lifshitz gravity with coupling constant $λ=1$. Our results show that the quasinormal frequencies depend on the parameter in the Hořava-Lifshitz gravity and the behavior of the quasinormal modes is different from those in the Reissner-Norstr\"{om} and Einstein-Born-Infeld black hole spacetimes. The absolute value of imaginary parts is smaller and the scalar perturbations decay more slowly in the deformed Hořava-Lifshitz black hole spacetime. This information can help us understand more about the Hořava-Lifshitz gravity.

gr-qc↗

arXiv2010

Improved parametrization of the growth index for dark energy and DGP models

We propose two improved parameterized form for the growth index of the linear matter perturbations: (I) $γ(z)=γ_0+(γ_{\infty}-γ_0){z\over z+1}$ and (II) $γ(z)=γ_0+γ_1 \frac{z}{z+1}+(γ_{\infty}-γ_1-γ_0)(\frac{z}{z+1})^α$. With these forms of $γ(z)$, we analyze the accuracy of the approximation the growth factor $f$ by $Ω^{γ(z)}_m$ for both the $ω$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 $Ω^{γ(z)}_m$ approximates the growth factor $f$ very well for all redshifts. For chosen $α$, the relative error is below 0.003% for the $Λ$CDM model and 0.028% for the DGP model when $Ω_{m}=0.27$. Thus, the second improved parameterized form of $γ(z)$ should be useful for the high precision constraint on the growth index of different models with the observational data. Moreover, we also show that $α$ depends on the equation of state $ω$ and the fractional energy density of matter $Ω_{m0}$, which may help us learn more information about dark energy and DGP models.

gr-qc↗

arXiv2010

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 the negative kinetic energy terms modifies the standard results in the greybody factor, super-radiance and Hawking radiation. Comparing with the usual scalar particle, the phantom scalar emission is enhanced in the black hole spacetime.

gr-qc↗

arXiv2009

Density pertubation of unparticle dark matter in the flat Universe

The unparticle has been suggested as a candidate of dark matter. We investigated the growth rate of the density perturbation for the unparticle dark matter in the flat Universe. First, we consider the model in which unparticle is the sole dark matter and find that the growth factor can be approximated well by $f=(1+3ω_u)Ω^γ_u$, where $ω_u$ is the equation of state of unparticle. Our results show that the presence of $ω_u$ modifies the behavior of the growth factor $f$. For the second model where unparticle co-exists with cold dark matter, the growth factor has a new approximation $f=(1+3ω_u)Ω^γ_u+αΩ_m$ and $α$ is a function of $ω_u$. Thus the growth factor of unparticle is quite different from that of usual dark matter. These information can help us know more about unparticle and the early evolution of the Universe.

gr-qc↗

arXiv2009

Dynamical evolution of scalar perturbation in Hořava-Lifshitz black-hole spacetimes

We study the dynamical evolution of a massless scalar perturbation in the Hořava-Lifshitz black-hole spacetimes with the coupling constants $λ={1/3}$, $λ={1/2}$ and $λ=3$, respectively. Our calculation shows that, for the three cases, the scalar perturbations decay without any oscillation in which the decay rate imprints the parameter of the Hořava-Lifshitz black hole. The results are quite different from those in the Schwarzschild AdS black hole and can help us understand more about the Hořava-Lifshitz gravity.

gr-qc↗

arXiv2009

The torsion cosmology in Kaluza-Klein theory

We have studied the torsion cosmology model in Kaluza-Klein theory. We considered two simple models in which the torsion vectors are $A_μ=(α,0,0,0)$ and $A_μ=a(t)^2(0,β,β,β)$, respectively. For the first model, the accelerating expansion of the Universe can be not explained without dark energy which is similar to that in the standard cosmology. But for the second model, we find that without dark energy the effect of torsion can give rise to the accelerating expansion of the universe and the alleviation of the well-known age problem of the three old objects for appropriated value of the model parameter $β$. These outstanding features of the second torsion cosmology model have been supported by the Type Ia supernovae (SNIa) data.

gr-qc↗