arXiv subjects

Songbai Chen

Publications and source records attributed to Songbai Chen.

At least 91 records · Page 5Linked to original sources

arXiv2017

Chaos in the motion of a test scalar particle coupling to Einstein tensor in Schwarzschild-Melvin black hole spacetime

We present firstly the equation of motion for a test scalar particle coupling to Einstein tensor in the Schwarzschild-Melvin black hole spacetime through the short-wave approximation. Through analysing Poincaré sections, the power spectrum, the fast Lyapunov exponent indicator and the bifurcation diagram, we investigate the effects of coupling parameter on the chaotic behavior of the particles. With the increase of the coupling strength, we find that the motion of coupled particle for the chosen parameters becomes more regular and order for the negative couple constant. While, for the positive one, the motion of coupled particles first undergoes a series of transitions between chaotic motion and regular motion and then falls into horizon or escapes to spatial infinite. Our results show that the coupling brings about richer effects for the motion of the particles.

gr-qc↗

arXiv2016

Strong gravitational lensing by a Konoplya-Zhidenko rotating non-Kerr compact object

Konoplya and Zhidenko have proposed recently a rotating non-Kerr black hole metric beyond General Relativity and make an estimate for the possible deviations from the Kerr solution with the data of GW 150914. We here study the strong gravitational lensing in such a rotating non-Kerr spacetime with an extra deformation parameter. We find that the condition of existence of horizons is not inconsistent with that of the marginally circular photon orbit. Moreover, the deflection angle of the light ray near the weakly naked singularity covered by the marginally circular orbit diverges logarithmically in the strong-field limit. In the case of the completely naked singularity, the deflection angle near the singularity tends to a certain finite value, whose sign depends on the rotation parameter and the deformation parameter. These properties of strong gravitational lensing are different from those in the Johannsen-Psaltis rotating non-Kerr spacetime and in the Janis-Newman-Winicour spacetime. Modeling the supermassive central object of the Milk Way Galaxy as a Konoplya-Zhidenko rotating non-Kerr compact object, we estimated the numerical values of observables for the strong gravitational lensing including the time delay between two relativistic images.

gr-qc↗

arXiv2016

Shadow casted by a twisted and rotating black hole

Zhang have obtained recently a twisted rotating black hole metric, which is a vacuum solution in four-dimensional Einstein gravity. This black hole solution has a rotation parameter, but without the total angular moment. Here, we have investigated the shadow casted by a twisted rotating black hole. Our results show that the shape of the shadow of the twisted rotating black hole is a standard round disk and does not depend on the inclination angle of the observer. It means that although the twisted rotating black hole has a rotation parameter, its shadow possesses the same behaviors as the common static black hole rather than the usual Kerr-like black holes. Moreover, we find that the marginally circular orbit radius of photon is independent of the direction of photon around the black hole. The value of the marginally circular orbit radius of photon and the size of shadow increase monotonously with the rotation parameter.

gr-qc↗

arXiv2016

Double shadow of a regular phantom black hole as photons couple to Weyl tensor

We have studied the shadow of a regular phantom black hole as photons couple to Weyl tensor. We find that the coupling yields that photons with different polarization directions propagate along different paths in the spacetime so that there exits double shadow for a black hole, which is quite different from that in the non-coupling case where only a single shadow emerges. The umbra of black hole increases with the phantom charge and decreases with the coupling strength. The dependence of the penumbra on the phantom charge and the coupling strength is converse to that of the umbra. Combining with the supermassive central object in our Galaxy, we estimated the shadow of the black hole as the photons couple to Weyl tensor. Our results show that the coupling brings richer behaviors of the propagation of coupled photon and the shadow of the black hole in the regular phantom black hole spacetime.

gr-qc↗

arXiv2016

Testing gravity of a regular and slowly rotating phantom black hole by quasi-periodic oscillations

We extend firstly the regular phantom black hole solution to a slowly rotating black hole case and find that the phantom field depresses the angular velocity of the event horizon and suppresses the super-radiation of black hole. We also probe the dependence of quasi-periodic oscillations frequencies in relativistic precession model on the phantom parameter. With the observation data of GRO J1655-40, we make a constraint on the parameters of the regular and slowly rotating phantom black hole. Our results show that although the best-fit value of the phantom parameter $b$ is small, the allowed value of $b$ in the $1σ$ region is $b<0.619$, which means that the phantom theoretical model can not be excluded by the constraint from quasi-periodic oscillations with the observation data of GRO J1655-40.

gr-qc↗

arXiv2016

Chaotic motion of particles in the accelerating and rotating black holes spacetime

We have investigated the motion of timelike particles along geodesic in the background of accelerating and rotating black hole spacetime. We confirmed that the chaos exists in the geodesic motion of the particles by Poincaré sections, the power spectrum, the fast Lyapunov exponent indicator and the bifurcation diagram. Moreover, we probe the effects of the acceleration and rotation parameters on the chaotic behavior of a timelike geodesic particle in the black hole spacetime. Our results show that the acceleration brings richer physics for the geodesic motion of particles.

gr-qc↗

arXiv2015

Black hole entropy arising from massless scalar field with Lorentz violation induced by the coupling to Einstein tensor

We have investigated quantum entropy of a static black hole arising from the massless scalar field with Lorentz violation induced by the coupling to Einstein tensor. Our results show that the coupled massless scalar field contributes to the classical Bekenstein-Hawking term in the black hole entropy. The corrected classical Bekenstein-Hawking entropy is not one quarter of the event horizon area of the original background black hole, but of a corresponding effective metric related to the coupling. It means that the classical Bekenstein-Hawking entropy depends not only on the black hole parameter, but also on the coupling which reduces Lorentz violation.

gr-qc↗

arXiv2015

Geometric optics for a coupling model of the electromagnetic and gravitational fields

The coupling between the electromagnetic and gravitational fields results in "faster than light" photons and invalids the Lorentz invariance and some laws of physics. A typical example is that the first and third laws of geometric optics are invalid in the usual spacetime. By introducing an effective spacetime, we find that the wave vector can be casted into null and then it obeys the geodesic equation, the polarization vector is perpendicular to the rays, and the number of photons is conserved. That is to say, the laws of geometric optics are still valid for the modified theory in the effective spacetime. We also show that the focusing theorem of light rays for the modified theory in the effective spacetime takes the same form as usual.

gr-qc↗

arXiv2015

Strong gravitational lensing for the photons coupled to Weyl tensor in a Schwarzschild black hole spacetime

We have investigated the strong gravitational lensing for the photons coupled to Weyl tensor in a Schwarzschild black hole spacetime. We find that in the four-dimensional black hole spacetime the equation of motion of the photons depends not only on the coupling between photon and Weyl tensor, but also on the polarization direction of the photons. It is quite different from that in the case of the usual photon without coupling to Weyl tensor in which the equation of motion is independent of the polarization of the photon. Moreover, we find that the coupling and the polarization direction modify the properties of the photon sphere, the deflection angle, the coefficients in strong field lensing, and the observational gravitational lensing variables. Combining with the supermassive central object in our Galaxy, we estimated three observables in the strong gravitational lensing for the photons coupled to Weyl tensor.

gr-qc↗

arXiv2015

Condensation for non-relativistic matter in Hořava-Lifshitz gravity

We study condensation for non-relativistic matter in a Hořava-Lifshitz black hole without the condition of the detailed balance. We show that, for the fixed non-relativistic parameter $α_2$ (or the detailed balance parameter $ε$), it is easier for the scalar hair to form as the parameter $ε$ (or $α_2$) becomes larger, but the condensation is not affected by the non-relativistic parameter $β_2$. We also find that the ratio of the gap frequency in conductivity to the critical temperature decreases with the increase of $ε$ and $α_2$, but increases with the increase of $β_2$. The ratio can reduce to the Horowitz-Roberts relation $ω_g/T_c\approx 8$ obtained in the Einstein gravity and Cai's result $ω_g/T_c\approx 13$ found in a Hořava-Lifshitz gravity with the condition of the detailed balance for the relativistic matter. Especially, we note that the ratio can arrive at the value of the BCS theory $ω_g/T_c\approx 3.5$ by taking proper values of $ε$, $α_2$, $β_2$ and $m$.

hep-th↗

arXiv2014

Dynamical evolution of a vector field perturbation coupling to Einstein tensor

We have investigated the wave dynamics of a vector field perturbation coupling to Einstein tensor in the four-dimensional Reissner-Nordström black hole spacetime. Our results show that besides the dependence on the coupling between the vector field and Einstein tensor, the wave dynamic equation of the vector field perturbation strongly depends on the parity of the perturbation itself, which is quite different from that of the usual vector field perturbation without the coupling in the four-dimensional spacetime. Moreover, we also find that the vector field perturbation with odd parity grows with exponential rate if the coupling strength is stronger than certain a critical value. However, the vector field perturbation with even parity always decays in the Reissner-Nordström black hole spacetime.

gr-qc↗

arXiv2014

Rotating charged black hole with Weyl corrections

We present firstly a four-dimensional spherical symmetric black hole with small Weyl corrections and find that with increasing Weyl corrections the region of the event horizon existence for the black hole in the parameter space increases for the negative Weyl coupling parameter and decreases for the positive one. Moreover, we also obtain a rotating charged black hole with weak Weyl corrections by the method of complex coordinate transformation. Our results show that the sign of Weyl coupling parameter $α$ yields the different spatial topology of the event horizons for the black hole with its parameters lied in some special regions in the parameter space. We also analyze the dependence of the ergosphere on the Weyl coupling parameter $α$ and find that with the increase of the Weyl corrections the ergosphere in the equatorial plane becomes thick for a black hole with $α>0$, but becomes thin in the case with $α<0$, which means that the energy extraction become easier in the background of a black hole with the positive Weyl coupling parameter, but more difficult in the background of a black hole with the negative one.

gr-qc↗

arXiv2014

Strong gravitational lensing in a rotating Kaluza-Klein black hole with squashed horizons

We have investigated the strong gravitational lensing in a rotating squashed Kaluza-Klein (KK) black hole spacetime. Our result show that the strong gravitational lensings in the rotating squashed KK black hole spacetime have some distinct behaviors from those in the backgrounds of the four-dimensional Kerr black hole and of the squashed KK Gödel black hole. In the rotating squashed KK black hole spacetime, the marginally circular photon radius $ρ_{ps}$, the coefficient $\bar{a}$, $\bar{b}$, the deflection angle $α(θ)$ in the $ϕ$ direction and the corresponding observational variables are independent of whether the photon goes with or against the rotation of the background, which is different with those in the usual four-dimensional Kerr black hole spacetime. Moreover, we also find that with the increase of the scale of extra dimension $ρ_0$, the marginally circular photon radius $ρ_{ps}$ and the angular position of the relativistic images $θ_\infty$ first decreases and then increases in the rotating squashed KK black hole for fixed rotation parameter $b$, but in the squashed KK Gödel black hole they increase for the smaller global rotation parameter $j$ and decrease for the larger one. In the extremely squashed case $ρ_0=0$, the coefficient $\bar{a}$ in the rotating squashed KK black hole increases monotonously with the rotation parameter, but in the squashed KK Gödel black hole it is a constant and independent of the global rotation of the Gödel Universe.

gr-qc↗

arXiv2013

Absorption cross section and Hawking radiation of the electromagnetic field with Weyl corrections

We have investigated the absorption cross section and the Hawking radiation of electromagnetic field with Weyl correction in the background of a four-dimensional Schwarzschild black hole spacetime. Our results show that the properties of the absorption cross section and the Hawking radiation depend not only on the Weyl correction parameter, but also on the parity of the electromagnetic field, which is quite different from those of the usual electromagnetic field without Weyl correction in the four-dimensional spacetime. With increase of Weyl correction parameter, the absorption probability, the absorption cross section, the power emission spectra and the luminosity of Hawking radiation decreases with Weyl correction parameter for the odd-parity electromagnetic field and increases with the event-parity electromagnetic field.

gr-qc↗

arXiv2013

Dynamical evolution of the electromagnetic perturbation with Weyl corrections

We present firstly the master equation of an electromagnetic perturbation with Weyl correction in the four-dimensional black hole spacetime, which depends not only on the Weyl correction parameter, but also on the parity of the electromagnetic field. It is quite different from that of the usual electromagnetic perturbation without Weyl correction in the four-dimensional spacetime. And then we have investigated numerically the dynamical evolution of the electromagnetic perturbation with Weyl correction in the background of a four-dimensional Schwarzschild black hole spacetime. Our results show that the Weyl correction parameter $α$ and the parities imprint in the wave dynamics of the electromagnetic perturbation. For the odd parity electromagnetic perturbation, we find it grows with exponential rate if the value of $α$ is below the negative critical value $α_c$. However, for the electromagnetic perturbation with even parity, we find that there does not exist such a critical threshold value and the electromagnetic field always decays in the allowed range of $α$.

gr-qc↗

arXiv2013

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

We present a slowly rotating black hole with phantom global monopole by solving Einstein's field equation and find that presence of global monopole changes the structure of black hole. The metric coefficient $g_{tϕ}$ contains 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 a deficit solid angle. Especially, the solid angle is surplus rather than deficit for a black hole with the phantom global monopole. We also study the correction originating from the global monopole to the angular velocity of the horizon $Ω_H$, the Kepler's third law, the innermost stable circular orbit and the radiative efficiency $ε$ in the thin accretion disk model. Our results also show that for the phantom black hole the radiative efficiency $ε$ is positive only for the case $η\leq η_c$. The threshold value $η_c$ increases with the rotation parameter $a$.

gr-qc↗

arXiv2013

$P-V$ criticality of AdS black hole in $f(R)$ gravity

We study thermodynamics of a charged AdS black hole in the special $f(R)$ correction with the constant Ricci scalar curvature. Our results show that the the $f(R)$ correction influences the Gibbs free energy and the phase transition of system. The ratio $ρ_c$ occurred at the critical point increases monotonically with the derivative term $f'(R_0)$. We also disclose that the critical exponents are the same as those of the liquid-gas phase transition in the Van der Waals model, which does not depend on the $f(R)$ correction considered here.

gr-qc↗

arXiv2013

Holographic superconductors in quintessence AdS black hole

We present a solution of Einstein equations describing a $d$-dimensional planar quintessence AdS black hole which depends on the state parameter $w_q$ of quintessence. We investigate holographic superconductors in this background and probe effects of the state parameter $w_q$ on the critical temperature $T_c$, the condensation formation and conductivity. The larger absolute value of $w_q$ leads to the lower critical temperature $T_c$ and the higher ratio between the gap frequency in conductivity to the critical temperature for the condensates. Moreover, we also find that the scalar condensate there exists an additional constraint condition originating from the quintessence $(d-1)w_q+λ_{\pm}>0$ for the operators $\mathcal{O}_{\pm}$, respectively. Our results show that the scalar condensation is harder to form and the occurrence of holographic dual superconductor needs the stronger coupling in the quintessence AdS black hole spacetime.

gr-qc↗