arXiv subjects

Jian-Bo Deng

Publications and source records attributed to Jian-Bo Deng.

At least 37 records · Page 2Linked to original sources

arXiv2020

Shadows of rotating Hayward-de Sitter black holes with astrometric observables

Motivated by recent work on rotating black hole shadow [Phys. Rev. D101, 084029 (2020)], we investigate the shadow behaviors of rotating Hayward-de Sitter black hole for static observers at a finite distance in terms of astronomical observables. This paper uses the newly introduced distortion parameter in [arXiv:2006.00685] to describe the shadow's shape quantitatively. We show that the spin parameter would distort shadows and the magnetic monopole charge would increase the degree of deformation. At the same time, the distortion could be relieved because of the cosmological constant and the distortion would increase with the distance from the black hole. Besides, the spin parameter, magnetic monopole charge and cosmological constant increase will cause the shadow to shrink.

gr-qc↗

arXiv2020

Optical properties of a nonlinear magnetic charged rotating black hole surrounded by quintessence with a cosmological constant

In this paper,we discuss optical properties of the nonlinear magnetic charged black hole surrounded by quintessence with a non-zero cosmological constant $Λ$. Setting the state parameter $ω=-3/2$ , we studied the horizon, the photon region and the shadow of this black hole. It turned out that for a fixed quintessential parameter $γ$, in a certain range, with the increase of the rotation parameter $a$ and magnetic charge $Q$, the inner horizon radius increases while the outer horizon radius decreases. And the cosmological horizon $r_Λ$ decrease when $γ$ or $Λ$ incease and increase slightly with increasing $a$ and $Q$. The shapes of photon region were then studied and depicted through graphical illustrations. Finally, we discussed the effects of the quintessential parameter $γ$ and the cosmological constant $Λ$ on the shadow cast by this balck hole with a fixed observer position.

gr-qc↗

arXiv2020

The cosmological constant from space-time discreteness

We regard the background of space-time as a physical system composed of discrete volume elements at the Planck scale and get the internal energy of space-time by Debye model. A temperature-dependent minimum energy limit of the particles is proposed from the thermal motion part of the internal energy. As decreases of the temperature caused by the expansion of the universe, more and more particles would be"released" because of the change of the energy limit, we regard these new particles as a source of dark energy. The minimum energy limit also leads to a corrected number of particles in universe and a modified conservation equation. According to the modified conservation equation, an effective cosmological constant consistent with its observed value is obtained.

gr-qc↗

arXiv2020

Optical properties of a Brane-World black hole as photons couple to the Weyl tensor

In this article, we have investigated the equations of motion of the photons coupled to Weyl tensor by the geometric optics approximation and the corresponding shadow in a Brane-World black hole spacetime. It is shown that there exists a double shadow for a black hole since the coupling photons with different polarization directions propagate along different paths in the spacetime. Furthermore, we discuss the effects of the metric parameter $α$ related to the cosmological constant, X-cold dark matter parameter $β$ and the coupling parameter $λ$ on the umbra (the overlap region of the double shadow) and the penumbra. We also obtain the finite-distance corrections to the deflection angle of light in the Brane-World black hole spacetime as the photons coupled to Weyl tensor by using a recent geometric method.

gr-qc↗

arXiv2019

Structure formation in the new Deser-Woodard nonlocal gravity model

We consider the structure formation in the nonlocal gravity model proposed recently by Deser and Woodard (DW-2019 model), which can not only reproduce the $Λ$CDM cosmology without fine-tuning puzzle but also may provide a screening mechanism for free. By using the direct numerical method of the reconstructing technique, the nonlocal distortion function $f(Y)$ is fixed as $f(Y)\simeq\boldsymbol{e}^{2.153(Y-16.97)}$ which has a small deviation with the fitted function proposed by Deser and Woodard. Based on the numerical results, we plotted the curve of the growth rate $fσ_8(z)$ under the DW-2019 model, which shows this model is not ruled out by the $fσ_8$ data from the Redshift-space distortions measurements. The evolving curve of the growth rate has a distinct plummet at $z\simeq0.39$, which is a great difference with the DW model. The possible reason is that the DW-2019 model provides the strong nonlocal effect, which behaves as the anisotropic effect to influence the matter perturbation in the low-redshift range. Finally the qualitative analysis of the screening mechanism is discussed by considering the spacial dependence of the nonlocal modification in the small-scale range.

astro-ph.CO↗

arXiv2019

Joule-Thomson expansion of the Bardeen-AdS black holes

The Joule-Thomson expansion process is studied for Bardeen-AdS black holes in the extended phase space. Firstly, we get Joule-Thomson coefficient and find that the divergent point of Joule-Thomson coefficient coincides with the zero point of temperature. The inversion curves are also obtained from the zero point of Joule-Thomson coefficient. Then the minimum inversion temperature and the corresponding mass are obtained. In addition, the ratio between minimum inversion and critical temperature for Bardeen-AdS black holes is also calculated. We obtain the isenthalpic curve in $T$-$P$ graph and demonstrate the cooling-heating region by the inversion curve. An interesting phenomenon we get is that black hole is always in heating process. The same phenomenon can be also obtained from the charged AdS black holes.

gr-qc↗

arXiv2019

The Varying Speed of Light in Eddington-inspired Born-Infield Gravity with Rainbow Metric

In this paper, we proposed that at each point of spacetime, in addition to the Riemannian metric tensor which describes the geometry of spacetime and the gravitational field, there is an rainbow metric tensor which shows the geometry of spacetime depends on the energy of the test particle. Because Eddington-inspired Born-Infield(EiBI) gravity can be seen as a special bi-metric gravity, we research a varying speed of light theory for a bi-metric gravity corresponding to EiBI gravity. For FRW universe, we find the energy of test particle will increase with rising energy density of universe. We also research the varying speed of light for three different kinds of rainbow functions and find the sign of parameter $κ$ would influence the trend of spend of light.

gr-qc↗

arXiv2019

Thermodynamics of charged AdS black holes in rainbow gravity

In this paper, the thermodynamic property of charged AdS black holes is studied in rainbow gravity. By the Heisenberg Uncertainty Principle and the modified dispersion relation, we obtain deformed temperature. Moreover, in rainbow gravity we calculate the heat capacity in a fixed charge and discuss the thermal stability. We also obtain a similar behaviour with the liquid-gas system in extending phase space (including $P$ and $r$) and study its critical behavior with the pressure given by the cosmological constant and with a fixed black hole charge $Q$. Furthermore, we study the Gibbs function and find its characteristic swallow tail behavior, which indicates the phase transition. We also find there is a special value about the mass of test particle which would lead the black hole to zero temperature and a diverging heat capacity with a fixed charge.

gr-qc↗

arXiv2019

Apparent horizon and gravitational thermodynamics of Universe in the Eddington-Born-Infeld theory

The thermodynamics of Universe in the Eddington-Born-Infeld (EBI) theory was restudied by utilizing the holographic-style gravitational equations that dominate the dynamics of the cosmical apparent horizon $Υ_{A}$ and the evolution of Universe. We started in rewriting the EBI action of the Palatini approach into the Bigravity-type action with an extra metric $q_{μν}$. With the help of the holographic-style dynamical equations, we discussed the property of the cosmical apparent horizon $Υ_{A}$ including timelike, spacelike and null characters, which depends on the value of the parameter of state $w_{m}$ in EBI Universe. The unified first law for the gravitational thermodynamics and the total energy differential for the open system enveloped by $Υ_{A}$ in EBI Universe were obtained. Finally, applying the positive-heat-out sign convention, we derived the generalized second law of gravitational thermodynamics in EBI universe.

gr-qc↗

arXiv2018

The evolution of universe in the two-scalar theory

We generalize f(R,T) gravity into the two-scalar theory that includes two independent scalar fields by the variational method, and we derive its field equations in Einstein frame using conformal transformation. Based on Friedmann equations and Raychaudhuri equation, with a consideration of the cosmic content as its perfect-fluid form, a further discussion leads us to an accelerated expanding condition of universe. In the two-scalar theory, universe has two states which are the accelerated expansion and decelerated contraction, and it has three stages during its evolution. The first and third stages are in the accelerated expanding state, and the second stage is in the decelerated contracting state. The third stage represents the present universe and it tends to become a dust universe.

gr-qc↗

arXiv2018

Discussion of a possible corrected black hole entropy

Einstein's equation could be interpreted as the first law of thermodynamic near the spherically symmetric horizon. Through recalling the Einstein gravity with a more general static spherical symmetric metric, we find that the entropy would have a correction in Einstein gravity. By using this method, we investigate the Eddington-inspired Born-Infeld (EiBI) gravity. Without matter field, we can also derive the first law in EiBI gravity. With an electromagnetic field, as the field equations have a more general spherically symmetric solution in EiBI gravity, we find that correction of the entropy could be generalized to EiBI gravity. Furthermore, we point out that the Einstein gravity and EiBI gravity might be equivalent on the event horizon. At last, under EiBI gravity with the electromagnetic field, a specific corrected entropy of black hole is given.

gr-qc↗

arXiv2017

Conformal transformation route to gravity's rainbow

Conformal transformation as a mathematical tool has been used in many areas of gravitational physics. In this paper, we would consider the gravity's rainbow, in which the metric could be treated as a conformal rescaling of the original metric. By using the conformal transformation technique, we get a specific form of modified Newton's constant and cosmological constant in gravity's rainbow, which implies that the total vacuum energy is dependent on probe energy. Moreover, the result shows that the Einstein gravity's rainbow could be described by an energy-dependent $f(E,\tilde R)$ gravity. At last, we study the $f(R)$ gravity, when the gravity's rainbow is considered, it can also be described as another energy-dependent $\tilde f(E,\tilde R)$ gravity.

gr-qc↗

arXiv2017

Hawking radiation-quasinormal modes correspondence for large AdS black holes

It is well-known that the non-strictly thermal character of the Hawking radiation spectrum generates a natural correspondence between Hawking radiation and black hole quasinormal modes. This main issue has been analyzed in the framework of Schwarzschild black holes, Kerr black holes and nonextremal Reissner-Nordstrom black holes. In this paper, by introducing the effective temperature, we reanalysis the non-strictly thermal character of large AdS black holes. The results show that the effective mass corresponding to the effective temperature is approximatively the average one in any dimension. And the other effective quantities can also be obtained. Based on the known forms of frequency in quasinormal modes, we reanalysis the asymptotic frequencies of the large AdS black hole in three and five dimensions. Then we get the formulas of the Bekenstein-Hawking entropy and the horizon's area quantization with functions of the quantum "overtone" number $n$.

gr-qc↗

arXiv2016

Quantum Cosmology via Quantization of Point-Like Lagrangian

The purpose of this paper is to introduce a new way to inquire the quantum cosmology for a certain gravitational theory. Normally, the quantum cosmological model is introduced as the minisuperspace theory which is obtained by reducing the superspace where the Wheel-DeWitt equation is defined on using the symmetry provided by cosmological principle. Unlike that, the key of our approach is to reinterpret the cosmology in a classical dynamical way using a point-like Lagrangian and then quantize the point-like model. We apply the method into Einstein gravity, gravity with a cosmological constant and the $f(R)$-gravity, and get their wave equations respectively. By analsysing the exact solution for the quantum cosmology with and without a cosmological constant we demonstrate that the cosmological constant is essential and being a tiny positive number. We also show the possibility of explaining inflation under the quantum version of cosmology.

gr-qc↗

arXiv2016

First-principle study on compensated half metallic double perovskite compound $Ba_2PrVO_6$

The first-principle study on double perovskite compound Ba$_2$PrVO$_6$ has been presented in this paper. By analysing band structures and integrated density of states, it is found that Ba$_2$PrVO$_6$ is ferromagnetic metallic within LSDA and compensated half metallic whithin LSDA+U. According to the total and partial density of states, the anti-ferromagnetism of Ba$_2$PrVO$_6$ is originated from the spin down state Pr$^{4+}$ ($4f_{-2}$) and the spin up hybridized state between the partially filled $t_{2g}$ state of V and the partially filled triple-degeneration state $4f_{-1}$, $4f_{+1}$, $4f_{+3}$ of Pr. We have investigated the magnetic evaluation of Ba$_2$PrVO$_6$ through fixed spin moment calculations, and the results indicate that the compensated half-metallic state is the ground state. The thermodynamic properties of Ba$_2$PrVO$_6$ are also studied by employing the quasi-harmonic Debye model.

cond-mat.mtrl-sci↗

arXiv2015

A model of eternal accelerated expansion without particle horizon

In our previous paper \cite{8}, we proposed a cosmological model from the emergence of space, which possesses a significant character of evaluating the vacuum energy from the Hubble constant and the age of universe. And one problem of this model is that there is no inflation in the early universe. In this paper, we aim at resolving this problem which leads us to a rather surprising conclusion that our cosmological model can avoid the horizon and flatness problems.

gr-qc↗

arXiv2015

A cosmological model from emergence of space

Many studies have been carried out since T.Padmanabhan proposed that the cosmic acceleration can be understood from the perspective that spacetime dynamics is an emergent phenomenon. Motivated by such a new paradigm, we firstly study the de Sitter universe from emergence of space. After that we investigate the universes in general cases and then narrow down our discussions into one of them with a detailed discussion of the possibility in describing our real universe classically. Furthermore, a constraint on $Ht$ and a estimated value of $\tildeΩ_Λ$ (caused by $ρ_{vac}$) can be derived from our model, the comparison with experiments is also presented. The results show the validity of our model.

gr-qc↗

arXiv2015

Half-metallic ferromagnetism in the RbSe and CsTe compounds with CsCl structure: A first-principles study

We investigate the electronic structures and magnetic properties of RbSe and CsTe compounds in CsCl, RS and ZB structures by using first-principles calculation. It is shown that these two compounds exhibit half-metallic ferromagnetism with an integer magnetic moment of 1.00 $μ_B$ per formula in all the three structures. Total energy calculations indicate the CsCl phase is more stable than the other two phases. We investigate these two compounds with CsCl structure in detail. The ferromagnetism results mainly from the spin-polarization of p states of anion Se (Te) for the two compounds. The half-metallicities of RbSe and CsTe compounds can be preserved up to 2.5\% and 0.8\% compression of lattice constants with respect to their equilibrium lattices, respectively.

cond-mat.mtrl-sci↗