José Carlos Olvera
The absorption section of black holes surrounded by scalar fields is studied with the sinc approximation in the eikonal limit. The effects of the scalar field on the nonlinear Euler-Heisenberg, the magnetic Bardeen and Reissner-Nordstrom BHs are studied in order to obtain information about how the scalar field affects different BHs.
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Basing on the ideas used by Kiselev, we study three black holes surrounded by quintessence and the effects of quintessence on the classical and semiclassical scattering cross-sections. In contrast, the absorption section is studied with the sinc approximation in the eikonal limit. For Schwarzschild, Reissner-Nordström and Bardeen black holes surrounded by quintessence, the values critical of charges and the normalization factor are obtained. We also described the horizons and the extremal condition of the black holes surrounded by quintessence. By setting for the quintessence state parameter i…
Shadow, absorption and Hawking radiation of a Schwarzschild black hole surrounded by a cloud of strings in Rastall gravity
本文研究Rastall引力中弦云包围的Schwarzschild黑洞，分析参数$a$和$β$对阴影、吸收截面及Hawking辐射的影响，发现负参数$β$使光子球和阴影半径呈N形变化，且弦参数$a$抑制辐射功率并延长黑洞寿命。
Scattering and absorption of a charged massive scalar field by a Reissner-Nordström black hole surrounded by perfect fluid dark matter
研究带电质量粒子撞击由完美流体暗物质（PFDM）包围的Reissner-Nordström（RN）黑洞时的散射，通过匹配方法在低频极限下近似得到吸收截面，并在高频极限下推导出弱场偏转角的二次项。数值结果与经典近似和荣耀散射一致，分析了暗物质、粒子电荷和质量对散射和吸收的影响。结果表明，随着暗物质参数λ增加，黑洞的吸收截面被强烈抑制，其高频极限仅依赖于黑洞电荷Q和λ。在超辐射极限下，PFDM黑洞的放大因子远大于RN黑洞。最后讨论了吸收截面在ω/m→1时的行为以及小散射角下的散射截面行为。
In this paper, we study the scattering and absorption sections of the Schwarzschild--anti de Sitter black hole surrounded by quintessence. The critical values of the cosmological constant and the normalization factor are obtained. We describe the event horizons and the extremal condition of the black hole surrounded by quintessence. The effects of quintessence on the classical and semi--classical scattering cross--sections have been estimated. Also, the absorption section is studied with the sinc approximation in the eikonal limit. We consider the quintessence state parameter in the particular…
We study scalar perturbations and quasinormal modes of a nonlinear magnetic charged black hole surrounded by quintessence. Time evolution of scalar perturbations is studied for different parameters associated with the black hole solution. We also study the reflection and transmission coefficients along with absorption cross-section for the considered black hole spacetime. It was shown that the real part of quasinormal frequency increases with increase in nonlinear magnetic charge while the module of the imaginary part of the frequency decreases. The analysis of the perturbations with changing …
Quasinormal modes and absorption cross-section of a Bardeen black hole surrounded by perfect fluid dark matter in four dimensions
本文研究了被完美流体暗物质包围的四维Bardeen黑洞的有质量标量场与无质量Dirac场扰动，利用三阶WKB方法计算了准正规模频率及吸收截面，并分析了暗物质参数、磁荷和标量场质量对结果的影响。
The expression of the impact parameter, in the analysis for classical and semiclassical scattering cross sections for black holes, is obtained with nonlinear electrodynamics (NLED) while the absorption section is studied with the sinc approximation in the eikonal limit considering NLED. As an illustration, we calculate the classical and semiclassical scattering as well as the absorption sections for three black holes under NLED, the regular magnetic Bardeen and Bronnikov black holes and the singular Euler-Heisenberg black hole. All are compared with the sections of their linear electromagnetic…
We consider a d-dimensional spherically symmetric dilatonic R^2 string corrected black hole solution. We study its stability under tensor type gravitational perturbations and compute the absorption cross section for low frequency gravitational waves.
The absorption cross section of rotating black holes in the Randall-Sundrum brane-world scenario for massless scalar waves is obtained via the partial-wave method. A variety of incidence directions with respect to the black hole rotation axis is considered. Special attention is given to near-extreme black holes, in which cases the absorption cross section increases as the tidal charge becomes more negative. It is shown that black holes with different configurations can present capture cross sections/shadows of same size. However, in such cases, the absorption spectra are different mainly for s…
We study scalar perturbations in the background of a Topological Lifshitz black hole in four dimensions. We compute analytically the quasinormal modes and from these modes we show that Topological Lifshitz black hole is stable. On the other hand, we compute the reflection and transmission coefficients and the absorption cross section and we show that there is a range of modes with high angular momentum which contributes to the absorption cross section in the low frequency limit. Furthermore, in this limit, we show that the absorption cross section decreases if the scalar field mass increases, …
The behavior of a charged scalar field in the RN black hole space time is studied using WKB approximation. In the present work it is assumed that matter waves can get reflected from the event horizon. Using this effect, the Hawking temperature and the absorption cross section for RN black hole placed in a charged scalar field are calculated. The absorption cross section $σ_{abs}$ is found to be inversely proportional to square of the Hawking temperature of the black hole.
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, th…
The nature of scalar wave functions near the horizon of Reissner Nordstrom (RN) extremal and Schwarzschild-de Sitter (SdS) extremal black holes are found using WKB approximation and the effect of reflection of waves from the horizon. The absorption cross section $σ_{abs}$ when RN extremal and SdS extremal black holes placed in a Klein-Gordon field is calculated.
Scattering and absorption sections by an improved Schwarzschild black hole
本文研究改进的Schwarzschild黑洞的散射与吸收截面，采用三种方法分析散射截面，发现量子修正影响干涉图案和振幅，吸收截面计算显示低频区域的偏差。
We consider planar massless scalar waves impinging upon a Kerr black hole, for general angles of incidence. We compute the absorption cross section via the partial wave approach, and present a gallery of results. In the low-frequency regime, we show that the cross section approaches the horizon area; in the high-frequency regime, we show that the cross section approaches the geodesic capture cross section. In the aligned case, we extend the complex angular momentum method to obtain a `sinc' approximation, which relates the regular high-frequency oscillations in the cross section to the propert…
Quantum-corrected Schwarzschild AdS black hole surrounded by quintessence: Thermodynamics and Shadows
本文研究了被暗能量物质包围的量子修正史瓦西AdS黑洞，分析了暗能量对Hawking温度、质量和比热的影响，并利用Carter方法考察了阴影半径随状态参数和归一化参数的变化规律及能量发射率。
We analytically study the scalar perturbation of non-asymptotically flat (NAF) rotating linear dilaton black holes (RLDBHs) in 4-dimensions. We show that both radial and angular wave equations can be solved in terms of the hypergeometric functions. The exact greybody factor (GF), the absorption cross-section (ACS), and the decay rate (DR) for the massless scalar waves are computed for these black holes (BHs). The results obtained for ACS and DR are discussed through graphs.
We investigate null geodesics impinging parallel to the rotation axis of a Kerr-Newman black hole, and show that the absorption cross section for a massless scalar field in the eikonal limit can be described in terms of the photon orbit parameters. We compare our sinc and low-frequency approximations with numerical results, showing that they are in excellent agreement.
In this work, we investigate the scattering of massless plane scalar waves by the high dimensional noncommutative Schwarzschild-Tangherlini black hole. We use the partial wave approach to determine the scattering and absorption cross sections in the incident wavelength range. Our numerical results demonstrate that the bigger the noncommutative parameter, the smaller the maximum value of the related partial absorption cross section, however the tendency is slightly. We also discovered that when the noncommutative parameter is weak, the absorption cross section of the high dimensional black hole…
Graybody factors and absorption cross-sections of non-exchange black holes in Instein-coupled scalar fields
研究非交换黑洞中与爱因斯坦张量耦合的标量场扰动，使用极化方法计算不同参数下的灰体因子和吸收截面，验证了灰体因子与准正态态的最新对应关系。
Gray-body factor and absorption of the Dirac field in ESTGB gravity
本文研究四维ESTGB引力中非线性电动力学模式下无质量Dirac场的灰体因子与吸收截面，用WKB和分波法计算，发现磁荷增大使灰体因子和总吸收截面减小，且Dirac场吸收对电荷更敏感。
In this paper, we have studied QNM modes and absorption cross sections of Born-Infeld-de Sitter black holes. WKB approximation is employed to compute the QNM modes of massless scalar fields. We have also used null geodesics to compute quasi-normal modes in the eikonal approximation. In the eikonal limit QNMs of black holes are determined by the parameters of the circular null geodesics. Unstable circular null orbits are derived from the effective metric which is obeyed by light rays under the influence of a nonlinear electromagnetic field. Comparison is shown with the QNM of the linear electro…
Long-lived quasinormal modes, grey-body factors and absorption cross-section of the black hole immersed in the Hernquist galactic halo
研究了黑洞在赫尔钦特暗物质晕中的拟正常模、灰体因子及吸收截面，发现场质量影响振荡频率和阻尼率，晕参数变化导致谱位移。
ModMax-black hole surrounded by cloud of strings in Bumblebee gravity
本文研究了ModMax黑洞周围环绕弦云在Bumblebee引力框架下的光学、热力学和散射特性，分析了黑洞的热力学性质，包括霍金温度、熵及其他相关热力学量，并探讨了不同扰动场在该黑洞背景中传播时的灰色体因子（GFs），评估了不同自旋场的吸收概率和能量辐射率，揭示了系统参数如洛伦兹对称破坏参数、弦云参数、ModMax参数、电荷和黑洞质量对辐射和散射过程的物理影响。
The effects of the tidal charge of black holes predicted in the Randall-Sundrum brane-world scenario on the electromagnetic cross sections and emission rate is studied. Although quantitatively different, the cross sections and emission rates of such black holes are similar to the ones of Schwarzschild black holes. The increase of the tidal-charge intensity makes the absorption cross sections increase and the interference-fringe widths of the differential scattering cross sections narrow. The electromagnetic emission rate increases initially with the increase of the tidal-charge intensity, but …
Neutral test particle dynamics around the Bardeen-AdS black hole surrounded by quintessence dark energy
该文研究被quintessence暗能量包围的Bardeen-AdS黑洞周围中性试验粒子动力学，分析参数对黑洞视界、有效势及ISCO半径的影响，发现quintessence参数会引发粒子运动混沌且混沌随能量升高而增强。
Absorption and scattering of charged scalar waves by charged Horndeski black hole
本文使用近似几何法与分波法研究了带电 Horndeski 黑洞对带电标量场的吸收与散射，发现其截面高于 Reissner-Nordström 黑洞，并揭示了超辐射对散射的增强作用。
Grey-body factors and absorption cross-sections of scalar and Dirac fields in the vicinity of dilaton-de Sitter black hole
研究稀顿-德西特黑洞附近标量和狄拉克场的传播特性，通过WKB近似计算灰体因子和吸收截面，揭示了不同参数对透射率的影响及总截面的高频和低频行为。
Greybody Factors, Absorption Cross Sections and Hawking Radiation of Holonomy-Corrected Schwarzschild Black Holes
通过数值积分和WKB近似，研究了圈量子引力启发的完整约束修正Schwarzschild黑洞上标量、电磁和狄拉克场的灰体因子、吸收截面和霍金辐射，发现完整约束修正增强了低能标量透射但整体抑制了霍金辐射。
We derive the absorption cross section of a minimally coupled scalar in the Lifshitz black hole obtained from the new massive gravity. The absorption cross section reduces to the horizon area in the low energy and massless limit of s-wave mode propagation, indicating that the Lifshitz black hole also satisfies the universality of low energy absorption cross section for black holes.
Absorption and scattering of massless scalar waves by black holes in quasi-topological gravity
研究准拓扑引力中正则黑洞对无质量标量波的吸收与散射，发现参数α增大使总吸收截面减小，且时空维度D的影响与先前计算不同。
Quasi-normal modes and absorption section from regular black holes immersed in perfect fluid dark matter
研究了浸没在完美流体暗物质中的正则黑洞的准正常模和吸收截面，揭示了PFDM对黑洞动态特性的影响。
Gravitational perturbations of Dymnikova black holes: grey-body factors and absorption cross-sections
研究Dymnikova正则黑洞的轴向引力扰动，计算灰体因子和吸收截面，验证准正常频率与传输系数的对应关系，发现量子参数影响仅在事件视界附近，导致灰体因子和吸收截面有微小偏差，Hawking辐射谱主要由修正的Hawking温度决定。
We study fermionic perturbations in the background of a two and five-dimensional dilatonic black holes. Then, we compute the reflection and transmission coefficients and the absorption cross section for fermionic fields, and we show numerically that the absorption cross section vanishes in the low and high frequency limit. Also we find that beyond a certain value of the horizon radius $r_0$ the absorption cross section for five-dimensional dilatonic black hole is constant. Besides, we have find that the absorption cross section decreases for higher angular momentum, and it decreases when the m…
Spectral lines of dirty wormholes
研究脏虫洞周围物质壳对无质量标量场吸收的影响，发现新的光环和准束缚态，表明天体物理环境无法掩盖虫洞的特征。
In this work, we numerically investigate the scattering and absorption cross section of the massless scalar field from some well-known regular black holes by using the partial wave approach. Our computational results indicate that the larger the parameters, the lower the associated total absorption cross section maxima. When compared to the Schwarzschild black hole, the scattering cross section is enhanced in some regular black hole spacetimes, meanwhile the scattering width is narrow in the forward orientation. Moreover, it is found that the null geodesics of the critical impact parameter and…
Accretion of fields by black holes is a subject of great interest in physics. It is known that accretion plays a fundamental role in active galactic nuclei and in the evolution of black holes. Accretion of fundamental fields is often related to the study of absorption cross section. Basically all black holes for which absorption of fields has been studied so far present singularities. However, even within general relativity, it is possible to construct regular black holes: objects with event horizons but without singularities. Many physically motivated regular black hole solutions have been pr…
In this paper we study the effects of black hole mass on the absorption cross section for a massive scalar field propagating in a 5-dimensional topological Chern-Simons black hole at the low-frequency limit. We consider the two branches of black hole solutions $(α=\pm 1)$ and we show that, if the mass of black hole increase the absorption cross section decreases at the zero-frequency limit for the branch $α=-1$ and for the other branch, $α=1$, the behavior is opposite, if the black hole mass increase the absorption cross section increases. Also we find that beyond a certain frequency value, th…
Black holes are a paradigm in nowadays physics, and are expected to be hosted at the center of galaxies. Supermassive galactic black holes are not isolated, and their surroundings play crucial roles in many observational features. The absorption and scattering of fields by isolated black holes have been vastly studied, allowing the understanding of many phenomenological features. However, as far as we are aware, a study of the influence of the presence of matter surrounding black holes in its planar wave scattering and absorption spectrum is still lacking in the literature. This may be importa…
We consider the propagation of a generic scalar field around a rotating and charged black hole. Using the partial wave method, we find, numerically, the total and partial absorption cross sections for different incidence angles. We investigate the low- and high-frequency limits, finding semi-analytical approximations for the absorption cross section, which we compare with our numerical results. Finally, we consider the superradiant regime, showing that, for charged fields, planar waves can be superradiantly scattered.
We calculate the absorption cross section of a massive neutral scalar field impinging upon a Reissner-Nordström black hole. First, we derive key approximations in the high- and low-frequency regimes. Next, we develop a numerical method to compute the cross section at intermediate frequencies, and present a selection of results. Finally, we draw together our complementary approaches to give a quantitative full-spectrum description of absorption.
In this paper we compute the low energy absorption cross-section for minimally coupled massles scalars and spin-$1/2$ particles, into a general spherically symmetric black hole in arbitrary dimensions. The scalars have a cross section equal to the area of the black hole, while the spin-$1/2$ particles give the area measured in a flat spatial metric conformally related to the true metric.
The absorption cross section is studied in the low-frequency region for a propagating scalar field under the warped AdS$_3$ black hole background in the topologically massive gravity. It can be shown that the absorption cross section is significantly deformed by the gravitational Chern-Simons term, which is proportional to the scattering area of black hole with an additional contribution depending on the left-moving and right-moving temperatures. It means that the cross section is larger than the area in spite of the s-wave limit. Finally, we discuss the left-right quasinormal modes for the sc…
Black holes are among the most intriguing objects in nature. They are believed to be fully described by General Relativity (GR), and the astrophysical black holes are expected to belong to the Kerr family, obeying the no-hair theorems. Alternative theories of gravity or parameterized deviations of GR allow black hole solutions, which have additional parameters other than mass and angular momentum. We analyze a Schwarzschild-like metric, proposed by Johannsen and Psaltis, characterized by its mass and a deformation parameter. We compute the absorption cross section of massless scalar waves for …
We investigate the absorption of planar massless scalar waves by a charged rotating stringy black hole, namely a Kerr--Sen black hole. We compute numerically the absorption cross section and compare our results with those of the Kerr-Newman black hole, a classical general relativity solution. In order to better compare both charged black holes, we define the ratio of the black hole charge to the extreme charge as $Q$. We conclude that Kerr--Sen and Kerr-Newman black holes have a similar absorption cross section, with the difference increasing for higher values of $Q$.
On-axis absorption and scattering of charged massive scalar waves by Kerr-Newman black-bounce spacetime
研究电荷质量标量波在Kerr-Newman黑洞- bounce空间时间沿旋转轴的吸收和散射特性，揭示旋转参数对超辐射的抑制作用及参数对能量提取效率的影响。
We discuss the phenomenology of massless scalar fields around a regular Bardeen black hole, namely absorption cross section, scattering cross section and quasinormal modes. We compare the Bardeen and Reissner-Nordström black holes, showing limiting cases for which their properties are similar.
The ratio of the low-energy absorption cross section for Dirac fermion to that for minimally coupled scalar is computed when the spacetimes are various types of the higher-dimensional Reissner-Nordström black holes. It is found that the low-energy absorption cross sections for the Dirac fermion always goes to zero in the extremal limit regardless of the detailed geometry of the spacetime. The physical importance of our results is discussed in the context of the brane-world scenarios and string theories.
In terms of the complex angular momentum method, we compute the absorption cross section by analyzing a massless test scalar field around conformally related black holes. At first, we investigate circular null geodesics and thereby prove a precondition for calculating the absorption cross section in the context of conformally related black holes. Then we use the WKB approximation method to derive the analytic expression of Regge frequency and the oscillation part of absorption cross sections. We find that this oscillation part depends on the scale factor of conformal transformations. By taking…
We investigate the absorption cross section of planar scalar massless waves impinging on spherically symmetric black holes which are solutions of the novel 4D Einstein-Gauss-Bonnet theory of gravity. Besides the mass of the black hole, the solution depends also on the Gauss-Bonnet constant coupling. Using the partial waves approach, we show that the absorption cross section depends on the Gauss-Bonnet coupling constant. Our numerical results present excellent agreement with the low- and high- frequency approximations, including the so-called sinc approximation.
Bonanno-Reuter regular black hole: quasi-resonances, grey-body factors and absorption cross-sections of a massive scalar field
研究有质量标量场在量子修正的 Bonanno-Reuter 规则黑洞背景下的准正态模式，发现场质量增加会抑制阻尼率并产生准共振，同时灰体因子随质量增加而减小。
We investigate the low-frequency absorption cross section of the electromagnetic waves for the extreme Reissner-Nordstrom black holes in higher dimensions. We first construct the exact solutions to the relevant wave equations in the zero-frequency limit. In most cases it is possible to use these solutions to find the transmission coefficients of partial waves in the low-frequency limit. We use these transmission coefficients to calculate the low-frequency absorption cross section in five and six spacetime dimensions. We find that this cross section is dominated by the modes with l=2 in the sph…
We investigate the absorption of a massive and charged scalar field in a Reissner-Nordström background. We compare our numerical results for the absorption cross section, obtained for arbitrary frequencies, with the low- and high-frequency limits. We find, in particular, that the total absorption cross section can be negative, showing that planar scalar waves can be superradiantly amplified by black holes.
Matter around Schwarzschild black holes in scalar-tensor theories: Absorption and Scattering
研究Schwarzschild黑洞在标量-张量理论中的吸收与散射机制，揭示不同模型下吸收和散射截面随参数变化的规律。
Massive Scalar Quasinormal Modes, Greybody Factors, and Absorption Cross Section of a Parity-Symmetric Beyond-Horndeski Black Hole
研究基于奇性对称超越霍恩德斯奇黑洞背景，探讨巨量标量场的准正常模、灰体因子及吸收截面，发现标量质量影响有效势，改变环谱与散射特性，且大质量范围下弱阻尼模式难以分离，巨量尾部主导，揭示场质量与几何变形的微妙交互。
We continue to study the response of black-hole space-times on the presence of additional strong sources of gravity. Restricting ourselves to static and axially symmetric (electro-)vacuum exact solutions of Einstein's equations, we first considered the Majumdar--Papapetrou solution for a binary of extreme black holes in a previous paper, while here we deal with a Schwarzschild black hole surrounded by a concentric thin ring described by the Bach--Weyl solution. The geometry is again revealed on the simplest invariants determined by the metric (lapse function) and its gradient (gravitational ac…
Absorption cross section in gravity's rainbow from confluent Heun equation
本文利用合流 Heun 方程连接系数及 Nekrasov-Shatashvili 自由能瞬子部分，研究引力彩虹背景下带电非旋转黑洞对无质量标量场的散射，并给出低能吸收截面的渐近展开。
We study the absorption of massive spin-half particles by a small Schwarzschild black hole by numerically solving the single-particle Dirac equation in Painleve-Gullstrand coordinates. We calculate the absorption cross section for a range of gravitational couplings Mm/m_P^2 and incident particle energies E. At high couplings, where the Schwarzschild radius R_S is much greater than the wavelength lambda, we find that the cross section approaches the classical result for a point particle. At intermediate couplings we find oscillations around the classical limit whose precise form depends on the …
In this paper we consider the solution of a black hole with a global monopole in $f(R)$ gravity and apply the partial wave approach to compute the differential scattering cross section and absorption cross section. We show that in the low-frequency limit and at small angles the contribution to the dominant term in the scattering/absorption cross section is modified by the presence of the global monopole and the gravity modification. In such limit, the absorption cross section shows to be proportional to the area of the event horizon.
We consider the absorption problem for a massless scalar field propagating in static and spherically symmetric black holes of arbitrary dimension endowed with a photon sphere. For this wide class of black holes, we show that the fluctuations of the high-energy absorption cross section are totally and very simply described from the properties (dispersion relation and damping) of the waves trapped near the photon sphere and therefore, in the eikonal regime, from the characteristics (orbital period and Lyapunov exponent) of the null unstable geodesics lying on the photon sphere. This is achieved …
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