arXiv subjects

Juhua Chen

Publications and source records attributed to Juhua Chen.

12 recordsLinked to original sources

arXiv2026

Massless scalar scattering by Kerr-Bertotti-Robinson black holes:transparent-end channels and superradiance

We formulate and numerically solve the real-frequency scattering problem for a neutral, minimally coupled, massless scalar on the rotating Kerr--Bertotti--Robinson (Kerr--BR) black-hole geometry, using a specified transparent boundary condition at the coordinate end. Since the Maxwell stress tensor of the background is traceless, the minimally coupled wave equation reduces to the four-dimensional conformal wave equation, enabling exact Carter-like separation after scaling the scalar field by the conformal factor. Unlike the asymptotically flat case, the coordinate end $r\to\infty$ lies at a finite tortoise distance. We show that the resulting reflection data are conditional on this boundary prescription rather than defining a unique, observer-independent cross section. Within the transparent-end model,open-channel superradiance is governed by a double-gate mechanism requiring both the local horizon condition and the outer propagation condition $q_\infty^2>0$. At the benchmark spin $a/M=0.9$, the co-rotating dipole amplification decreases as the external magnetic field increases. Crucially, the field narrows and closes the open superradiant window at $BM\simeq0.243$. Near the propagation threshold, the amplification coefficient vanishes linearly with the outer wave number.

gr-qc↗

arXiv2026

Thermodynamical phase structures and particle emission rate of charged AdS black hole surrounded by string cloud and quintessence via shadow formalism

In this paper, the shadow of the four-dimensional charged AdS black hole surrounded by string cloud and quintessence is derived. The shadow radius shows a strictly monotonic and invertible correlation with the event horizon radius. The phase structures of the black hole for different parameters are reproduced through traditional thermodynamic geometry, which are similar to a van der Waals system. By analyzing the phase structure of the black hole in the context of shadows, thermodynamical phase structures with the shadow radius as the variable replicate the phase transition with the event horizon radius as the variable. We present the energy emission rates for massless and massive particles and discover that the maximum emission frequency can also serve as a useful tool for thermodynamic analysis. We firstly study and systematically establish shadow thermodynamics under the background of string cloud and quintessence, and our results reveal the independent regulatory mechanism of dark components on phase transitions as well as the universal topological invariance of the phase transition structure.

gr-qc↗

arXiv2026

Scattering and absorption of a charged massive scalar field by a Reissner-Nordström black hole surrounded by perfect fluid dark matter

We study the scattering of charged massive particles impinging on a Reissner-Nordström (RN) black hole immersed in perfect fluid dark matter (PFDM). We obtain an approximation of absorption cross section in the low-frequency regime via the matching method. In the high-frequency regime, we derive the weak-field deflection angle up to second order. The numerical results are in excellent agreement with classical approximation and glory scattering. The effects of dark matter, particle charge, and mass upon scattering and absorption are examined in detail. The results show that as the dark matter parameter $λ$ increases, the absorption cross section of the black hole is strongly suppressed, and its high-frequency limit depends only on the black hole charge $Q$ and $λ$. The scattering cross section also decreases overall. In the superradiant regime, the amplification factor of the PFDM black hole is much larger than that of the RN black hole. Finally, we discuss the behavior of the absorption cross section as $ω/m\rightarrow1$, as well as the scattering cross section at small scattering angles.

gr-qc↗

arXiv2025

MMCE: A Framework for Deep Monotonic Modeling of Multiple Causal Effects

When we plan to use money as an incentive to change the behavior of a person (such as making riders to deliver more orders or making consumers to buy more items), the common approach of this problem is to adopt a two-stage framework in order to maximize ROI under cost constraints. In the first stage, the individual price response curve is obtained. In the second stage, business goals and resource constraints are formally expressed and modeled as an optimization problem. The first stage is very critical. It can answer a very important question. This question is how much incremental results can incentives bring, which is the basis of the second stage. Usually, the causal modeling is used to obtain the curve. In the case of only observational data, causal modeling and evaluation are very challenging. In some business scenarios, multiple causal effects need to be obtained at the same time. This paper proposes a new observational data modeling and evaluation framework, which can simultaneously model multiple causal effects and greatly improve the modeling accuracy under some abnormal distributions. In the absence of RCT data, evaluation seems impossible. This paper summarizes three priors to illustrate the necessity and feasibility of qualitative evaluation of cognitive testing. At the same time, this paper innovatively proposes the conditions under which observational data can be considered as an evaluation dataset. Our approach is very groundbreaking. It is the first to propose a modeling framework that simultaneously obtains multiple causal effects. The offline analysis and online experimental results show the effectiveness of the results and significantly improve the effectiveness of the allocation strategies generated in real world marketing activities.

cs.LG↗

arXiv2014

Spinning Particle in Gravitational Field of Black Hole Involving Global Monopole

In this paper we study the dynamics of trajectory of a spinning particle in a Schwarzschild spacetime involving a global monopole. We set up the equations of motion and find three types of trajectories. We study the conditions that a spinning particle, originally moving in the innermost stable circular orbit around the black hole involving a global monopole, will escape to infinity after it is kicked by another particle or photon. Three types of trajectories of a spinning particle in a Schwarzschild spacetime involving a global monopole are simulated in detail and the escaping energy and velocity of the spinning particle is also obtained in the present paper.

gr-qc↗

arXiv2014

Geodesic structure of Janis-Newman-Winicour space-time

In the present paper we study the geodesic structure of the Janis-Newman-Winicour(JNW) space-time which contains a strong curvature naked singularity. This metric is an extension of the Schwarzschild geometry when a massless scalar field is included. We find that the strength parameter $μ$ of the scalar field effects on the geodesic structure of the JNW space-time. By solving the geodesic equation and analyzing the behavior of effective potential, we investigate all geodesic types of the test particle and the photon in the JNW space-time. At the same time we simulate all the geodesic orbits corresponding to the energy levels of the effective potential in the JNW space-time.

gr-qc↗

arXiv2013

Distribution of Entropy of Bardeen Regular Black Hole with Corrected State Density

We consider corrections to all orders in the Planck length on the quantum state density, and calculate the statistical entropy of the scalar field on the background of the Bardeen regular black hole numerically. We obtain the distribution of entropy which is inside the horizon of black hole and the contribution of the vicinity of horizon takes a great part of the whole entropy.

gr-qc↗

arXiv2011

Geodesic Structure of Test Particle in Bardeen Spacetime

The Bardeen model describes a regular space-time, i.e. a singularity-free black hole space-time. In this paper, by analyzing the behavior of the effective potential for the particles and photons, we investigate the time-like and null geodesic structures in the space-time of Bardeen model. At the same time, all kinds of orbits, which are allowed according to the energy level corresponding to the effective potentials, are numerically simulated in detail. We find many-world bound orbits, two-world escape orbits and escape orbits in this spacetime. We also find that bound orbits precession directions are opposite and their precession velocities are different, the inner bound orbits shift along counter-clockwise with high velocity while the exterior bound orbits shift along clockwise with low velocity.

gr-qc↗

arXiv2011

Scattering of Scalar Waves by Schwarzschild Black Hole Immersed in Magnetic Field

The magnetic field is one of the most important constituents of the cosmic space and one of the main sources of the dynamics of interacting matter in the universe. The astronomical observations imply the existence of a strong magnetic fields of up to $10^4-10^8G$ near supermassive black holes in the active galactic nuclei and even around stellar mass black holes. In this paper, with the quantum scattering theory, we analysis the Schröedinger-type scalar wave equation of black hole immersed in magnetic field and numerically investigate its absorption cross section and scattering cross section. We find that the absorption cross sections oscillate about the geometric optical value in the high frequency regime. Furthermore in low frequency regime, the magnetic field makes the absorption cross section weaker and this effect is more obviously on lower frequency brand. On the other hand, for the effects of scattering cross sections for the black hole immersed in magnetic field, we find that the magnetic field makes the scattering flux weaker and its width narrower in the forward direction. We find that there also exists the glory phenomenon along the backforward direction. At fixed frequency, the glory peak is higher and the glory width becomes narrower due to the black hole immersed in magnetic field.

gr-qc↗

arXiv2009

Timelike Geodesic Motion in Horava-Lifshitz Spacetime

Recently Ho$\breve{r}$ava proposed a non-relativistic renormalisable theory of gravitation. When restricted to satisfy the condition of detailed balance, this theory is intimately related to topologically massive gravity in three dimensions, and the geometry of the Cotton tensor. At long distances, this theory is expected to flow to the relativistic value $λ= 1$, and could therefore serve as a possible candidate for a UV completion of Einstein general relativity or an infrared modification thereof. In this paper under allowing the lapse function to depend on the spatial coordinates $x^i$ as well as $t$, we obtain the spherically symmetric solutions. And then by analyzing the behavior of the effective potential for the particle, we investigate the timelike geodesic motion of particle in the Ho$\breve{r}$ava-Lifshitz spacetime. We find that the nonradial particle falls from a finite distance to the center along the timelike geodesics when its energy is in an appropriate range. However, we find that it is complexity for radial particle along the timelike geodesics. There are follow different cases due to the energy of radial particle: 1) When the energy of radial particle is higher than a critical value $E_{C}$, the particle will fall from infinity to the singularity directly; 2) When the energy of radial particle equals to the critical value $E_{C}$, the particle orbit is unstable at $r=r_{C}$, i.e. the particle will escape from $r=r_{C}$ to the infinity or to the singularity, which is determined by the initial conditions of the particle; 3) When the energy of radial particle is in a proper range, the particle will rebound to the infinity or plunge to the singularity from a infinite distance, which is also determined by the initial conditions of the particle.

gr-qc↗

arXiv2009

Evolution of the interacting viscous dark energy model in Einstein cosmology

In this paper we investigate the evolution of the viscous dark energy (DE) interacting with the dark matter (DM) in the Einstein cosmology model. Using the linearizing theory of the dynamical system, we find, in our model, there exists a stable late time scaling solution which corresponds to the accelerating universe, and we also find the unstable solution under some appropriate parameters. In order to alleviate the coincidence problem, some authors considered the effect of quantum correction due to the conform anomaly and the interacting dark energy model. But if we take into account the bulk viscosity of the cosmic fluid, the coincidence problem will be softened just like the interacting dark energy cosmology model. That's to say, both the non-perfect fluid model and the interacting models of the dark energy can alleviate or soften the singularity of the universe.

gr-qc↗

arXiv2009

Quasinormal Modes of Scalar Field in Five-dimensional Lovelock Black Hole Spacetime

In this paper using the third-order WKB approximation, a numerical method devised by Schutz, Will and Iyer, we investigate the quasinormal frequencies of the scalar field in the background of five-dimensional Lovelock black hole. We find that the ultraviolet correction to Einstein theory in the Lovelock theory makes the scalar field decay more slowly and makes the scalar field oscillate more quickly, and the cosmological constant makes the scalar field decay more slowly and makes the scalar field oscillate more slowly in Lovelock black hole backgroud. On the other hand we also find that quasinormal frequencies depend very weakly on the angular quantum number $l$.

gr-qc↗