arXiv subjects

Hongbo Cheng

Publications and source records attributed to Hongbo Cheng.

At least 37 records · Page 2Linked to original sources

arXiv2015

The description of phase transition of Bardeen black hole in the Ehrenfest scheme

The phase transition of a Bardeen black hole is studied by considering Ehrenfest's equations. The thermodynamic variables such as entropy, potential and heat capacity are calculated from the first law of thermodynamics for black holes. That no discontinuity in entropy and potential of the black holes means that the first order phase transition will not generate for the Bardeen black holes. However, the divergence of heat capacity at constant potential and satisfaction of the Ehrenfest's equations indicates that the second order phase transition of Bardeen black hole will appear.

hep-th↗

arXiv2015

The description of phase transition in a black hole with conformal anomaly in the Ehrenfest's scheme

We make use of the Ehrenfest's equation to explore the phase transition of a black hole with conformal anomaly. The first order phase transition is ruled out because no discontinuity appears in entropy of the black holes. We find that the phase transition of black holes belong to the second order subject to the Ehrenfest's equations. Further we also show that the second order phase transition will not happen for the black holes without conformal anomaly.

hep-th↗

arXiv2015

The deflection angle of a gravitational source with global monopole in the strong field limit

We investigate the gravitational lensing effect in the strong field background around the Schwarzschild black hole with extremely small mass and solid deficit angle subject to the global monopole by means of the strong field limit issue. We obtain the angular position and magnification of the relativistic images and show that they relate to the global monopole parameter $η$. We discuss that with the increase of parameter $η$, the minimum impact parameter $u_{m}$ and angular separation $s$ increase and the relative magnification $r$ decreases. We also find that $s$ grows extremely greatly as the increasing parameter $η$ becomes large enough. The effect from the solid deficit angle is the dependence of angular position, angular separation and relative magnification on parameter $η$, which may offer a way to characterize some possible distinct signatures of the Schwarzschild black hole with a solid deficit angle associated with global monopole.

hep-th↗

arXiv2015

The analytical discussion on strong gravitaional lensing for a gravitational source with a $f(R)$ global monopole

Here the gravitational lensing in strong field limit of a Schwarzschild black hole with a solid deficit angle owing to global monopole within the context of the $f(R)$ gravity theory is investigated. We obtain the expressions of deflection angle and time delay in the forms of elliptic integrals and discuss the asymptotic behaviour of the elliptic integrals to find the explicit formulae of angle and time difference in the strong field limit. We show that the deflection angle and the time delay between multiple images are related not only to the monopole but also to the $f(R)$ correction $ψ_{0}$ by taking the cosmological boundary into account. Some observables such as the minimum impact parameter, the angular separation, the relative magnification and the compacted angular position have been estimated as well. It is intriguing that the tiny modification on the standard general relativity will make the remarkable deviation on the angle and the time lag, offering a significant way to explore some possible distinct signatures of the topological soliton and the correction of the Einstein general relativity.

gr-qc↗

arXiv2015

The greybody factor for scalar fields in the Schwarzschild spacetime with an $f(R)$ global monopole

The greybody factor of massless scalar fields in the four-dimensional Schwarzschild spacetime involving an $f(R)$ global monopole is derived. We show how the monopole parameter and the deviation from the standard general relativity adjust the greybody factor. We also demonstrate that the effects from the global monopole and $f(R)$ gravity theory are manifest in the energy emission rate and the generalized absorption cross section of the scalar fields.

hep-th↗

arXiv2015

The strong field gravitational lensing in the Schwarzschild black hole pierced by a cosmic string

In this work the gravitational lensing in the strong field limit around the Schwarzschild black hole pierced by a cosmic string is studied. We find that the deflection angle and the time delay of the relativistic images depend on the tension of cosmic string. It is interesting that the deflection angle is greater when the tension of cosmic string is stronger. The time delay between two images is more obvious in the case of weaker tension.

gr-qc↗

arXiv2015

The virial relation for the Q-balls in the thermal logarithmic potential revisited analytically

We study the properties of Q-balls dominated by the thermal logarithmic potential analytically instead of estimating the characters with only some specific values of model variables numerically. In particular the analytical expressions for radius and energy of this kind of Q-ball are obtained. According to these explicit expressions we demonstrate strictly that the large Q-balls enlarge and the small ones become smaller in the background with lower temperature. The energy per unit charge will not be divergent if the charge is enormous. We find that the lower temperature will lead the energy per unit charge of Q-ball smaller. We also prove rigorously the necessary conditions that the model parameters should satisfy to keep the stability of the Q-balls. When one of model parameters of Q-balls $K$ is positive, the Q-balls will not form or survive unless the temperature is high enough. In the case of negative $K$, the Q-balls are stable no matter the temperature is high or low.

hep-th↗

arXiv2014

The time delay in strong gravitational lensing with Gauss-Bonnet correction

The time delay between two relativistic images in the strong gravitational lensing governed by Gauss-Bonnet gravity is studied. We derive and calculate the expression of time delay due to the Gauss-Bonnet coupling. It is shown that the time delay for two images with larger space each other is longer. We also find that the ratio of Gauss-Bonnet coefficient and the mass of gravitational source changes in the region like $\fracα{M}\in[0,2)$. The time delay is divergent with $\fracα{M}\longrightarrow 2$.

gr-qc↗

arXiv2013

The proximity force approximation for the Casimir energy of plate-sphere and sphere-sphere systems in the presence of one extra compactified universal dimension

The Casimir energies for plate-sphere system and sphere-sphere system under PFA in the presence of one extra compactified universal dimension are analyzed. We find that the Casimir energy between a plate and a sphere in the case of sphere-based PFA is divergent. The Casimir energy of plate-sphere system in the case of plate-based PFA is finite and keeps negative. The extra-dimension corrections to the Casimir energy will be more manifest if the sphere is larger or farther away from the plate. It is shown that the negative Casimir energy for two spheres is also associated with the sizes of spheres and extra space. The larger spheres and the longer distance between them make the influence from the additional dimension stronger.

hep-th↗

arXiv2013

The calculation of the thermodynamic quantities of the Bardeen black hole

In this work we research on the thermodynamical properties of the Bardeen black holes. We compute the series of new thermodynamic quantities such as local temperature, heat capacity, off-shell free energy of this kind of black hole in detail. We further analyze the thermodynamical characteristics of the Bardeen black hole by varying its charge $q$ to check the existence and stability of the black hole.

hep-th↗

arXiv2013

The thermodynamic quantities of a black hole with an $f(R)$ global monopole

The thermodynamic quantities such as the local temperature, heat capacity, off-shell free energy and the stability of a black hole involving a global monopole within or outside the $f(R)$ gravity are examined. We compare the two classes of results to show the influence from the generalization of the general relativity. It is found that the $f(R)$ theory will modify the thermodynamic properties of black holes, but the shapes of curves for thermodynamic quantities with respect to the horizon are similar to the results within the frame of general relativity. In both cases there will exist a small black hole which will decay and a large stable black hole in the case that the temperatures are higher than their own critical temperature.

hep-th↗

arXiv2012

The evolution of circular loops of a cosmic string with periodic tension

In this paper the equation of circular loops of cosmic string with periodic tension is investigated in the Minkowski spacetime and Robertson-Walker universe respectively. We find that the cosmic string loops possessing this kind of time-varying tension will evolve to oscillate instead of collapsing to form a black hole if their initial radii are not small enough.

hep-th↗

arXiv2011

The virial relation for compact Q-balls in the complex signum-Gordon model

In this work the properties of Q-balls in the complex signum-Gordon model in $d$ spatial dimensions is studied. We obtain a general virial relation for this kind of Q-ball in the higher-dimensional spacetime. We compute the energy and radii of Q-ball with V-shaped field potential as a function of spatial dimensionality and a parameter defining the model potential energy density.

hep-th↗

arXiv2011

The Casimir force on a piston at finite temperature in Randall-Sundrum models

The Casimir effect for a three-parallel-plate system at finite temperature within the frame of five-dimensional Randall-Sundrum models is studied. In the case of Randall-Sundrum model involving two branes we find that the Casimir force depends on the plates distance and temperature after one outer plate has been moved to the distant place. Further we discover that the sign of the reduced force is negative as the plate and piston locate very close, but the reduced force nature becomes repulsive when the plates distance is not very tiny and finally the repulsive force vanishes with extremely large plates separation. The thermal influence causes the repulsive Casimir force greater. Within the frame of one-brane scenario the reduced Casimir force between the piston and one plate left keeps attractive no matter how high the temperature is. It is interesting that the thermal effect leads the attractive Casimir force greater instead of changing the force nature.

hep-th↗

arXiv2011

The Casimir effect for parallel plates at finite temperature in the presence of one fractal extra compactified dimension

We discuss the Casimir effect for massless scalar fields subject to the Dirichlet boundary conditions on the parallel plates at finite temperature in the presence of one fractal extra compactified dimension. We obtain the Casimir energy density with the help of the regularization of multiple zeta function with one arbitrary exponent and further the renormalized Casimir energy density involving the thermal corrections. It is found that when the temperature is sufficiently high, the sign of the Casimir energy remains negative no matter how great the scale dimension $δ$ is within its allowed region. We derive and calculate the Casimir force between the parallel plates affected by the fractal additional compactified dimension and surrounding temperature. The stronger thermal influence leads the force to be stronger. The nature of the Casimir force keeps attractive.

hep-th↗

arXiv2011

The Casimir effect for parallel plates in the spacetime with a fractal extra compactified dimension

The Casimir effect for massless scalar fields satisfying Dirichlet boundary conditions on the parallel plates in the presence of one fractal extra compactified dimension is analyzed. We obtain the Casimir energy density by means of the regularization of multiple zeta function with one arbitrary exponent. We find a limit on the scale dimension like $δ>1/2$ to keep the negative sign of the renormalized Casimir energy which is the difference between the regularized energy for two parallel plates and the one with no plates. We derive and calculate the Casimir force relating to the influence from the fractal additional compactified dimension between the parallel plates. The larger scale dimension leads to the greater revision on the original Casimir force. The two kinds of curves of Casimir force in the case of integer-numbered extra compactified dimension or fractal one are not superposition, which means that the Casimir force show whether the dimensionality of additional compactified space is integer or fraction.

hep-th↗

arXiv2010

The Casimir effect for parallel plates involving massless Majorana fermions at finite temperature

We study the Casimir effect for parallel plates with massless Majorana fermions obeying the bag boundary conditions at finite temperature. The thermal influence will modify the effect. It is found that the sign of the Casimir energy keeps negative if the product of plate distance and the temperature is larger than a special value or the energy will change to be positive. The Casimir energy rises with the stronger thermal influence. We show that the attractive Casimir force between two parallel plates becomes greater with the increasing temperature. In the case of piston system involving the same Majorana fermions with the same boundary conditions, the attractive force on the piston will weaker in the hotter surrounding.

hep-th↗

arXiv2010

The Casimir force on a piston in Randall-Sundrum models

The Casimir effect of a piston for massless scalar fields which satisfy Dirichlet boundary conditions in the context of five-dimensional Randall-Sundrum models is studied. In these scenarios we derive and calculate the expression for the Casimir force on the piston. We also discuss the Casimir force in the limit that one outer plate is moved to the remote place to show that the nature of the reduced force between the parallel plates left. In the Randall-Sundrum model involving two branes the two plates attract each other when they locate very close, but the reduced Casimir force turns to be repulsive as the plates separation is not extremely tiny, which is against the experimental phenomena. In the case of one brane model the shape of the reduced Casimir force is similar to that of the standard two-parallel-system in the four-dimensional flat spacetimes while the sign of force remains negative.

hep-th↗