arXiv subjects
Publications and source records attributed to De-Cheng Zou.
In scalar-tensor theories, compact objects may experience spontaneous scalarization. Recently, it was shown that matter-induced spontaneous scalarization of neutron stars is predominantly associated with a first-order phase transition. Here we consider matter-induced spontaneous scalarization of boson stars. Employing a repulsive quartic potential for the bosonic matter, we find only first-order phase transitions.
Th spontaneous scalarization of the Einstein-Euler-Heisenberg (EEH) black hole is performed in the EEH-scalar theory by introducing an exponential scalar coupling (with $α$ coupling constant) to the Maxwell term.Here, the EEH black hole as a blad black hole is described by mass $M$ and magnetic charge $q$ with an action parameter $μ$. A choice of $μ=0.3$ gurantees a single horizon with unrestricted magnetic charge $q$. The onset scalarization of this black hole appears for a positive coupling $α$ with an unlimited magnetic charge $q$. However, there exists a difference between $q\le1$ and $q>1$ onset scalarizations. We notify the presence of infinite branches labeled by the number of $n=0,1,2,\cdots$ of scalarized charged black holes by taking into account the scalar seeds around the EEH black hole. We find that the $n=0$ fundamental branch of all scalarized black holes is stable against the radial perturbations, while the $n=1$ excited branch is unstable.
In this paper, we investigate massive charged scalar perturbations in four-dimensional charged Lifshitz-AdS black holes with scalar hair, within the framework of Einstein--Maxwell--Dilaton (EMD) gravity. Using the improved asymptotic iteration method (AIM), we compute the quasinormal modes (QNMs) and explore their dependence on key parameters, including the Lifshitz dynamical exponent $z$, the scalar field mass and charge, and the black hole charge, under various spatial curvature settings ($k=0, \pm1$). Our results reveal rich and sensitive behavior in both the real and imaginary parts of QNMs. In particular, the decay rates can exhibit monotonic or non-monotonic dependence on the black hole charge, depending on the values of $z$, $m_s$, and $q_s$. These findings highlight the significant role of field and geometric parameters in governing the dynamical stability of Lifshitz black holes and offer insights into the perturbative properties of non-AdS holographic systems.
In this paper, we study the perturbations of massless scalar and electromagnetic fields on the magnetically charged black holes in string-inspired Euler-Heisenberg theory. We calculate the quasinormal frequencies (QNFs) and discuss influences of black hole magnetic charge $Q_m$, coupling parameter $ε$ and angular momentum $l$ on QNFs, emphasizing the relationship between these parameters and QNMs behavior. We find these results obtained through the AIM method are in good agreement with those of obtained by WKB method. The greybody factor is calculated by WKB method. The effects of these parameters $Q_m$ and $ε$ on the greybody factor are also studied.
In the present work, we investigate the gravitational lensing effects of two quantum-modified black hole models recently proposed in effective quantum gravity. The light deflection angles are calculated for both the weak-field and strong-field limits. Furthermore, using the data for the supermassive black holes SgrA* and M87*, we calculate the lensing observables in the strong-field limit. We find that the quantum parameter plays a role analogous to the electric charge in weak gravitational lensing. In the strong-field limit, in contrast, the effects of the quantum parameter on the deflection angle, the angular separation, and the relative magnification are opposite to those of the electric charge, the scalar charge, and the quantum parameters in some gravity theories. The results indicate the crucial difference between the classical black holes and the two quantum-modified black hole models that depend on the quantum correction, making them a valuable tool for distinguishing these black hole models.
In this paper, we explore the quasinormal modes (QNMs) of a black hole surrounded by a fluid of strings within the framework of Rastall gravity. We analyze the behavior of scalar, electromagnetic, and gravitational perturbations, focusing on the influence of the black hole charge $Q$ and angular momentum $l$ on the quasinormal frequencies. Our numerical results reveal a significant dependence on the parameter $\varepsilon$. These trends are consistent across different types of perturbations, emphasizing the relationship between black hole parameters and QNMs behavior.
We study the spontaneous scalarization of Bardeen black holes, whose tachyonic instability triggers the formation of scalarized charged black holes (SCBHs). In this case, we find infinite ($n=0,1,2,\cdots$) branches of SCBHs with magnetic charge $g$. The $n = 0$ branch of SCBHs can be found for the coupling parameter $α\geq α_{n=0}(g)$ with both quadratic (1-$αφ^2$) and exponential ($e^{-αφ^2}$) couplings, where $α_{n=0}(g)$ represents the threshold of tachyonic instability for the Bardeen black holes. Furthermore, it is shown that the $n = 0$ branch for both couplings is stable against radial perturbations. This stability shows that this branch can be used for further observational implications.
In this paper, we focus on massive Einstein-dilaton gravity including the coupling of dilaton scalar field to massive graviton terms, and then derive static and spherically symmetric solutions of charged dilatonic black holes in four dimensional spacetime. We find that the dilatonic black hole could possess different horizon structures for some suitably parameters. Then, we also investigate the thermodynamic properties of charged dilatonic black holes where $f(r)$ approaches $+\infty$ and $-\infty$, respectively.
Recently, an interesting \textit{doppelgänge} black hole solution is obtained in the string-inspired Euler-Heisenberg theory, where the black holes have the same radii but share different charges. We found, however, they possess different ISCOs and photon spheres, and hence affect their shadow images. In this work, we investigate the optical appearances, illuminated by an optically and geometrically thin disk, are investigated, of such black hole. One finds that doppelgänge black holes have different optical appearances. Even the horizon radii are the same, the size of shadows are not equal. Furthermore, we found that the large magnetic charge $Q_m$ black holes give rise to novel shadow images that the usual bright rings inside shadow are not clear, The optical appearances illuminated by spherically accretions are also examined, and it can also identify two doppelgänge black holes.
Considering the nonminimal coupling of the dilaton field to the massive graviton field in Maxwell-dilaton-massive gravity, we obtain a class of analytical solutions of charged black holes, which are neither asymptotically flat nor (A)dS. The calculated thermodynamic quantities, such as mass, temperature and entropy, verify the validity of the first law of black hole thermodynamics. Moreover, we further investigate the critical behaviors of these black holes in the grand canonical and canonical ensemble, and find a novel critical phenomenon never before observed, known as the ``reverse" reentrant phase transition with a tricritical point. It implies that the system undergoes a novel ``SBH-LBH-SBH" phase transition process, and is the reverse of the ``LBH-SBH-LBH" process observed in reentrant phase transitions.
In this work, we discuss the generalized Einstein-Maxwell-Dilaton gravity theory with a nonminimal coupling between the Maxwell field and scalar field. Considering different geometric properties of black hole horizon structure, the charged dilaton Lifshitz black hole solutions are presented in 4-dimensional spacetimes. Later, utilizing the Wald Formalism, we derive the thermodynamic first law of black hole and conserved quantities. According to the relationship between the heat capacity and the local stability of black hole, we study the stability of charged Lifshitz black holes and identify the thermodynamic stable region of black holes that meet the criteria.
In this paper, we focus on massive Einstein-dilaton gravity including the coupling of dilaton scalar field to massive graviton terms, and then derive static and spherically symmetric solutions of dilatonic black holes in four dimensional spacetime. We find that the dilatonic black hole could possess two horizons (event and cosmological), extreme (Nariai) and naked singularity for the suitably fixed parameters. In addition, we investigate thermodynamic properties of these dilatonic black holes, and check the corresponding first law of black hole thermodynamics. Extending to the massive Einstein-dilaton gravity in high dimensions, we further obtain the dilatonic black hole solutions in $(d+1)$ dimensional spacetime.
We investigate the tachyonic instability of Kerr-Newman (KN) black hole with a rotation parameter $a$ in the Einstein-Chern-Simons-scalar theory coupled with a quadratic massive scalar field. This instability analysis corresponds to exploring the onset of spontaneous scalarization for KN black holes. First, we find no $a$-bound for $α<0$ case by considering (1+1)-dimensional analytical method. A direct numerical method is adopted to explore (2+1)-dimensional time evolution of a massive scalar perturbation with positive and negative $α$ to obtain threshold curves numerically. We obtain threshold curves $α_{\rm th}(a)$ of tachyonic instability for positive $α$ without any $a$-bounds. We expect to find the same threshold curves $α_{\rm th}(a)$ of tachyonic instability for negative $α$ without any $a$-bound because its linearized scalar theory is invariant under the transformation of $α\to -α$ and $θ\to -θ$. In addition, it is found that the scalar mass term suppresses tachyonic instability of KN black holes.
We consider Einstein-Weyl gravity with a minimally coupled scalar field in four dimensional spacetime. By using the Minimal Geometric Deformation (MGD) approach, we split the highly nonlinear coupled field equations into two subsystems that describing the background geometry and scalar field source, respectively. Regarding the Schwarzschild-AdS metric as a background geometry, we derive analytical approximate solutions of scalar field and deformation metric functions with Homotopy Analysis Method (HAM), providing their analytical approximations to fourth order. Moreover, we discuss the accuracy of the analytical approximations, showing they are sufficiently accurate throughout the exterior spacetime.
In this paper, we discuss a fully nonlinear mechanism for the formation of scalarized rotating black holes in Einstein-scalar-Gauss-Bonnet gravity, where Kerr black holes are linearly stable, but unstable against nonlinear scalar perturbations. With the help of the pseudospectral method, we obtain a spectrum of nonlinearly scalarized rotating black hole solutions with multiple scalarized branches. Moreover, we investigate the thermodynamic properties of nonlinearly scalarized rotating black holes and find the phase transition between Kerr and these scalarized black holes.
The Homotopy Analysis Method (HAM) is a useful method to derive analytical approximate solutions of black holes in modified gravity theories. In this paper, we study the Einstein-Weyl gravity coupled with Maxwell field, and obtain analytical approximation solutions for charged black holes by using the HAM. It is found that the analytical approximate solutions are sufficiently accurate in the entire spacetime outside the black hole's event horizon, and also consistent with numerical ones for charged black holes in the Einstein-Maxwell-Weyl gravity.
The spontaneous scalarization of Schwarzscild-AdS is investigated in the Einstein-scalar-Gauss--Bonnet (ESGB) theory. Firstly, we construct scalarized AdS black holes numerically. Secondly, making use of the homotopy analysis method (HAM), we obtain analytical approximate solutions for scalarized AdS black holes in the ESGB theory. It is found that scalarized AdS black holes constructed numerically are consistent with analytical approximate solutions in the whole space.
In this study, the gravitational decoupling approach via extended geometric deformation is utilized to generate analytical black hole solutions owing to its simplicity and effectiveness. Considering the external fields surrounding Schwarzschild AdS black holes, we derive hairy black hole solutions in asymptotic AdS spacetime, satisfying the strong and dominant energy conditions. Moreover, we find that if the black hole spacetime is a fluid system, the fluid under each of these conditions is anisotropic.