Pub Date : 2024-08-23DOI: 10.1134/s0202289324700269
Z. Yousaf, M. Z. Bhatti, A. Farhat
Abstract
In the presence of an anisotropic fluid, we examine the irregularity factors for a spherically symmetric relativistic matter. In (f(mathcal{G},T^{2})) gravity, we investigate the equations of motion and dynamical relations using a systematic construction, where (T) stands for the trace of the energy-momentum tensor, and (mathcal{G}) is the Gauss–Bonnet term. With the use of the Weyl tensor, we examine two well-known differential equations that would lead to an analysis of the sources of inhomogeneities. In (f(mathcal{G},T^{2})) gravity, the irregularity factors are investigated by taking specific cases in the adiabatic and non-adiabatic regimes. We find that the conformal tensor and additional curvature terms compromise inhomogeneity for a pressureless nonradiating fluid and an isotropic fluid. In contrast to other cases, for a nonradiating anisotropic fluid, we observe that the term ((Pi+mathcal{E})) now accounts for the survival of density inhomogeneity, rather than just the Weyl tensor and the modified terms. The last case clearly illustrates how several components, namely, radiating terms, the fluid shear and the expansion scalar in the (f(mathcal{G},T^{2})) framework, are accountable for the formation of inhomogeneities from a homogeneous state of the structure. In the case (f(mathcal{G},T^{2})=0), all our results reduce to those of GR.
摘要 在存在各向异性流体的情况下，我们研究了球对称相对论物质的不规则系数。在(f(mathcal{G},T^{2}))引力中，我们使用系统结构研究了运动方程和动力学关系，其中(T)代表能动张量的迹，(mathcal{G})是高斯-波奈项。利用韦尔张量，我们研究了两个众所周知的微分方程，它们将导致对不均匀性来源的分析。在（f(mathcal{G},T^{2})）引力中，我们通过绝热和非绝热状态下的具体案例研究了不规则因子。我们发现，对于无压非辐射流体和各向同性流体，共形张量和附加曲率项会影响不均匀性。与其他情况不同的是，对于非辐射各向异性流体，我们观察到项（(Pi+mathcal{E})）现在解释了密度不均匀性的存续，而不仅仅是韦尔张量和修正项。最后一种情况清楚地说明了在(f(mathcal{G},T^{2}))框架中，辐射项、流体剪切力和膨胀标量这几个部分是如何从结构的均质状态形成不均匀性的。在 (f(mathcal{G},T^{2})=0) 的情况下，我们的所有结果都与 GR 的结果一致。
{"title":"Causes of Energy Density Inhomogeneity in Energy Momentum Squared Gravity","authors":"Z. Yousaf, M. Z. Bhatti, A. Farhat","doi":"10.1134/s0202289324700269","DOIUrl":"https://doi.org/10.1134/s0202289324700269","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>In the presence of an anisotropic fluid, we examine the irregularity factors for a spherically symmetric relativistic matter. In <span>(f(mathcal{G},T^{2}))</span> gravity, we investigate the equations of motion and dynamical relations using a systematic construction, where <span>(T)</span> stands for the trace of the energy-momentum tensor, and <span>(mathcal{G})</span> is the Gauss–Bonnet term. With the use of the Weyl tensor, we examine two well-known differential equations that would lead to an analysis of the sources of inhomogeneities. In <span>(f(mathcal{G},T^{2}))</span> gravity, the irregularity factors are investigated by taking specific cases in the adiabatic and non-adiabatic regimes. We find that the conformal tensor and additional curvature terms compromise inhomogeneity for a pressureless nonradiating fluid and an isotropic fluid. In contrast to other cases, for a nonradiating anisotropic fluid, we observe that the term <span>((Pi+mathcal{E}))</span> now accounts for the survival of density inhomogeneity, rather than just the Weyl tensor and the modified terms. The last case clearly illustrates how several components, namely, radiating terms, the fluid shear and the expansion scalar in the <span>(f(mathcal{G},T^{2}))</span> framework, are accountable for the formation of inhomogeneities from a homogeneous state of the structure. In the case <span>(f(mathcal{G},T^{2})=0)</span>, all our results reduce to those of GR.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700270
Faizuddin Ahmed, Abdelmalek Bouzenada
Abstract
In this research, we focus on investigating the behavior of zero-spin scalar boson-antiboson particles in a specific space-time of ((1+2))-dimensional circularly symmetric and static traversable wormhole with cosmic strings, all under the influence of a quantum flux field. We start by deriving the wave equation from the Klein–Gordon equation, which governs the relativistic quantum motion of scalar bosons-antibosons. By solving this equation using the confluent Heun equation, we obtain the ground state energy level (E^{+}_{1,ell}) and the corresponding wave function (Psi^{+}_{1,ell}) as a particular case. The main findings of this study indicate that various factors, such as the presence of cosmic strings, the radius of the wormhole throat, and the quantum flux, have significant impacts on the behavior of scalar bosons-antibosons.
{"title":"Effects of a Flux Field on Quantum Dynamics of Scalar Particles in Wormhole Background with Disclinations","authors":"Faizuddin Ahmed, Abdelmalek Bouzenada","doi":"10.1134/s0202289324700270","DOIUrl":"https://doi.org/10.1134/s0202289324700270","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>In this research, we focus on investigating the behavior of zero-spin scalar boson-antiboson particles in a specific space-time of <span>((1+2))</span>-dimensional circularly symmetric and static traversable wormhole with cosmic strings, all under the influence of a quantum flux field. We start by deriving the wave equation from the Klein–Gordon equation, which governs the relativistic quantum motion of scalar bosons-antibosons. By solving this equation using the confluent Heun equation, we obtain the ground state energy level <span>(E^{+}_{1,ell})</span> and the corresponding wave function <span>(Psi^{+}_{1,ell})</span> as a particular case. The main findings of this study indicate that various factors, such as the presence of cosmic strings, the radius of the wormhole throat, and the quantum flux, have significant impacts on the behavior of scalar bosons-antibosons.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209711","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700208
Elmo Benedetto, Luca D’Errico, Antonio Feoli
Abstract
During typical general relativity courses, the gravitational fields generated by rotating objects and the so-called frame dragging effect are explained by emphasizing the presence of a gravitational Coriolis-like force term. It is well known that, in a rotating system, there is also a fictitious centrifugal force. In general, textbooks do not discuss also the possibility of a gravitational centrifugal-like force, and, in a recent paper, we have analyzed the presence of a repulsive force in the vicinity of a rotating mass. Now, however, we want to reviews some historical aspects of Mach’s Principle and to analyze the centrifugal gravitational term inside a rotating spherical shell, with a new simple approach.
{"title":"Machian Effects Inside a Rotating Spherical Shell","authors":"Elmo Benedetto, Luca D’Errico, Antonio Feoli","doi":"10.1134/s0202289324700208","DOIUrl":"https://doi.org/10.1134/s0202289324700208","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>During typical general relativity courses, the gravitational fields generated by rotating objects and the so-called frame dragging effect are explained by emphasizing the presence of a gravitational Coriolis-like force term. It is well known that, in a rotating system, there is also a fictitious centrifugal force. In general, textbooks do not discuss also the possibility of a gravitational centrifugal-like force, and, in a recent paper, we have analyzed the presence of a repulsive force in the vicinity of a rotating mass. Now, however, we want to reviews some historical aspects of Mach’s Principle and to analyze the centrifugal gravitational term inside a rotating spherical shell, with a new simple approach.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209690","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700282
Archana Dixit, Anirudh Pradhan, K. Ghaderi
Abstract
This investigation focuses on a Bianchi type-V universe characterized by spatial homogeneity and anisotropy, wherein the cosmic medium consists of interacting dark matter and holographic dark energy. We obtain solutions to the field equations by considering the Hubble parameter (H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}}), and constrain the model parameters. Employing Bayesian analysis and likelihood functions in conjunction with the Markov Chain Monte Carlo (MCMC) method, we determine the following model parameters: (H_{0}=71.3388^{+0.00010}_{-0.00094}), and (n=-1.08147^{+0.00010}_{-0.00010}). In this study, we constrain the model parameters by using the joint datasets ((H(z)+textrm{BAO}+textrm{Pantheon})). We explain the physical and geometric aspects of the model. We also examine the behavior of the velocity of sound and different energy conditions to test the viability of our cosmological model.
摘要 本研究的重点是以空间均匀性和各向异性为特征的边奇型-V宇宙，其中宇宙介质由相互作用的暗物质和全息暗能量组成。我们通过考虑哈勃参数(H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}}/)得到场方程的解，并对模型参数进行约束。利用贝叶斯分析和似然函数，结合马尔可夫链蒙特卡罗（MCMC）方法，我们确定了以下模型参数：(H_{0}=71.3388^{+0.00010}_{-0.00094}), and (n=-1.08147^{+0.00010}_{-0.00010}).在这项研究中，我们利用联合数据集（(H(z)+textrm{BAO}+textrm{Pantheon}）来约束模型参数。）我们解释了模型的物理和几何方面。我们还研究了声速的行为和不同的能量条件，以检验我们的宇宙学模型的可行性。
{"title":"Interacting Bianchi Type-V Universe: Observational Constraints","authors":"Archana Dixit, Anirudh Pradhan, K. Ghaderi","doi":"10.1134/s0202289324700282","DOIUrl":"https://doi.org/10.1134/s0202289324700282","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>This investigation focuses on a Bianchi type-V universe characterized by spatial homogeneity and anisotropy, wherein the cosmic medium consists of interacting dark matter and holographic dark energy. We obtain solutions to the field equations by considering the Hubble parameter <span>(H(z)=(H_{0}/sqrt{2})sqrt{1+(1+z)^{2n}})</span>, and constrain the model parameters. Employing Bayesian analysis and likelihood functions in conjunction with the Markov Chain Monte Carlo (MCMC) method, we determine the following model parameters: <span>(H_{0}=71.3388^{+0.00010}_{-0.00094})</span>, and <span>(n=-1.08147^{+0.00010}_{-0.00010})</span>. In this study, we constrain the model parameters by using the joint datasets (<span>(H(z)+textrm{BAO}+textrm{Pantheon})</span>). We explain the physical and geometric aspects of the model. We also examine the behavior of the velocity of sound and different energy conditions to test the viability of our cosmological model.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s020228932470021x
Shahroud Azami, Mehdi Jafari
Abstract
We examine almost Riemann solitons and almost gradient Riemann solitons in generalized Robertson–Walker space-times and perfect fluid space-times. At first, we prove that if a generalized Robertson–Walker space-time admits an almost Riemann soliton or an almost gradient Riemann soliton, then it becomes a perfect fluid space-time. Next, we observe that a space-time with an almost Riemann soliton whose potential vector field, is a conformal vector field, is an Einstein manifold, and if the potential vector field is a nonhomothetic conformal vector field, then space-time is of Petrov type O or N. In final, we prove that if a generalized Robertson–Walker space-time satisfies the definition of an almost Riemann soliton, and (Q.P=0) then it is an Einstein manifold, and consequently it is a perfect fluid space-time.
摘要 我们研究广义罗伯逊-沃克时空和完美流体时空中的近黎曼孤子和近梯度黎曼孤子。首先，我们证明，如果广义罗伯逊-沃克时空中存在几乎黎曼孤子或几乎梯度黎曼孤子，那么它就成为完美流体时空。接下来，我们观察到，一个具有几乎黎曼孤子的时空，如果其势能向量场是共形向量场，那么它就是爱因斯坦流形；如果势能向量场是非同调共形向量场，那么它就是彼得罗夫 O 或 N 型时空。最后，我们证明，如果广义罗伯逊-沃克时空满足几乎黎曼孤子的定义，并且（Q.P=0），那么它就是爱因斯坦流形，因此它是完美流体时空。
{"title":"Riemann Solitons on Relativistic Space-Times","authors":"Shahroud Azami, Mehdi Jafari","doi":"10.1134/s020228932470021x","DOIUrl":"https://doi.org/10.1134/s020228932470021x","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We examine almost Riemann solitons and almost gradient Riemann solitons in generalized Robertson–Walker space-times and perfect fluid space-times. At first, we prove that if a generalized Robertson–Walker space-time admits an almost Riemann soliton or an almost gradient Riemann soliton, then it becomes a perfect fluid space-time. Next, we observe that a space-time with an almost Riemann soliton whose potential vector field, is a conformal vector field, is an Einstein manifold, and if the potential vector field is a nonhomothetic conformal vector field, then space-time is of Petrov type O or N. In final, we prove that if a generalized Robertson–Walker space-time satisfies the definition of an almost Riemann soliton, and <span>(Q.P=0)</span> then it is an Einstein manifold, and consequently it is a perfect fluid space-time.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209691","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700154
V. I. Dokuchaev
Abstract
We describe the possible forms of black hole images viewed by a distant observer (or a telescope) on the celestial sphere. These images are numerically calculated based on general relativity and the equations of motion in the Kerr–Newman metric. A black hole image is a gravitationally lensed image of the black hole event horizon. It may be viewed as a black spot on the celestial sphere, projected inside the position of a classical black hole shadow. In the nearest future it will be possible to verify modified gravity theories by observations of astrophysical black holes with Space Observatory Millimetron.
{"title":"Images of Black Holes Viewed by a Distant Observer","authors":"V. I. Dokuchaev","doi":"10.1134/s0202289324700154","DOIUrl":"https://doi.org/10.1134/s0202289324700154","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We describe the possible forms of black hole images viewed by a distant observer (or a telescope) on the celestial sphere. These images are numerically calculated based on general relativity and the equations of motion in the Kerr–Newman metric. A black hole image is a gravitationally lensed image of the black hole event horizon. It may be viewed as a black spot on the celestial sphere, projected inside the position of a classical black hole shadow. In the nearest future it will be possible to verify modified gravity theories by observations of astrophysical black holes with Space Observatory Millimetron.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209853","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700178
S. V. Bolokhov, K. A. Bronnikov, M. V. Skvortsova
Abstract
The widely discussed “black-bounce” mechanism of removing a singularity at (r=0) in a spherically symmetric space-time, proposed by Simpson and Visser, consists in removing the point (r=0) and its close neighborhood, resulting in emergence of a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce. Instead, it has been recently proposed to make (r=0) a regular center by properly modifying the metric, still preserving its form in regions far from (r=0). Different algorithms of such modifications have been formulated for a few classes of singularities. The previous paper considered space-times whose Ricci tensor satisfies the condition (R^{t}_{t}=R^{r}_{r}), and regular modifications were obtained for the Schwarzschild, Reissner-Nordström metrics, and two examples of solutions with magnetic fields obeying nonlinear electrodynamics (NED). The present paper considers regular modifications of more general space-times, and as examples, modifications with a regular center have been obtained for the Fisher (also known as JNW) solution with a naked singularity and a family of dilatonic black holes. Possible field sources of the new regular metrics are considered in the framework of general relativity (GR), using the fact that any static, spherically symmetric metric can be presented as a solution with a combined source involving NED and a scalar field with some self-interaction potential. This scalar field is, in general, not required to be of phantom nature (unlike the sources for black bounces), but in the examples discussed here, the possible scalar sources are phantom in a close neighborhood of (r=0) and are canonical outside it.
摘要辛普森（Simpson）和维瑟（Visser）提出的在球对称时空中消除奇点（r=0）的 "黑反弹 "机制引起了广泛讨论，该机制包括消除点（r=0）及其近邻，从而出现一个规则的球半径最小值，它可以是一个虫洞咽喉，也可以是一个规则的反弹。相反，最近有人提出通过适当修改度量，使(r=0)成为一个规则中心，同时在远离(r=0)的区域仍然保留其形式。针对几类奇点，人们提出了不同的修改算法。前一篇论文考虑了里奇张量满足条件(R^{t}_{t}=R^{r}_{r})的时空，并得到了施瓦兹柴尔德、雷斯纳-诺德斯特伦度量以及两个服从非线性电动力学（NED）的磁场解的正则修正。本文考虑了更一般时空的正则修正，并以具有裸奇点的费雪（也称 JNW）解和稀释黑洞系列为例，给出了具有正则中心的修正。我们在广义相对论（GR）框架下考虑了新规则度量的可能场源，利用了这样一个事实，即任何静态球面对称度量都可以呈现为一种解，其组合源涉及 NED 和具有某种自相互作用势的标量场。一般来说，这个标量场不需要是幻影性质的（与黑色反弹的源不同），但在这里讨论的例子中，可能的标量源在(r=0)的近邻中是幻影的，而在它（r=0）之外则是典型的。
{"title":"A Regular Center Instead of a Black Bounce","authors":"S. V. Bolokhov, K. A. Bronnikov, M. V. Skvortsova","doi":"10.1134/s0202289324700178","DOIUrl":"https://doi.org/10.1134/s0202289324700178","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The widely discussed “black-bounce” mechanism of removing a singularity at <span>(r=0)</span> in a spherically symmetric space-time, proposed by Simpson and Visser, consists in removing the point <span>(r=0)</span> and its close neighborhood, resulting in emergence of a regular minimum of the spherical radius that can be a wormhole throat or a regular bounce. Instead, it has been recently proposed to make <span>(r=0)</span> a regular center by properly modifying the metric, still preserving its form in regions far from <span>(r=0)</span>. Different algorithms of such modifications have been formulated for a few classes of singularities. The previous paper considered space-times whose Ricci tensor satisfies the condition <span>(R^{t}_{t}=R^{r}_{r})</span>, and regular modifications were obtained for the Schwarzschild, Reissner-Nordström metrics, and two examples of solutions with magnetic fields obeying nonlinear electrodynamics (NED). The present paper considers regular modifications of more general space-times, and as examples, modifications with a regular center have been obtained for the Fisher (also known as JNW) solution with a naked singularity and a family of dilatonic black holes. Possible field sources of the new regular metrics are considered in the framework of general relativity (GR), using the fact that any static, spherically symmetric metric can be presented as a solution with a combined source involving NED and a scalar field with some self-interaction potential. This scalar field is, in general, not required to be of phantom nature (unlike the sources for black bounces), but in the examples discussed here, the possible scalar sources are phantom in a close neighborhood of <span>(r=0)</span> and are canonical outside it.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209854","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s020228932470018x
Milena Skvortsova
Abstract
We investigate quasinormal ringing in both time and frequency domains for scalar and neutrino perturbations around black hole solutions that simultaneously describe regular and extreme configurations in the framework of nonlinear electrodynamics. Two types of solutions are considered: those with de Sitter and Minkowski cores. The quasinormal frequencies obtained from two independent methods exhibit excellent agreement. Furthermore, we derive an analytical expression in the eikonal limit and discuss the validity of the correspondence between the eikonal quasinormal modes and null geodesics.
{"title":"Ringing of Extreme Regular Black Holes","authors":"Milena Skvortsova","doi":"10.1134/s020228932470018x","DOIUrl":"https://doi.org/10.1134/s020228932470018x","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>We investigate quasinormal ringing in both time and frequency domains for scalar and neutrino perturbations around black hole solutions that simultaneously describe regular and extreme configurations in the framework of nonlinear electrodynamics. Two types of solutions are considered: those with de Sitter and Minkowski cores. The quasinormal frequencies obtained from two independent methods exhibit excellent agreement. Furthermore, we derive an analytical expression in the eikonal limit and discuss the validity of the correspondence between the eikonal quasinormal modes and null geodesics.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209855","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700257
K. K. Ernazarov, V. D. Ivashchuk
Abstract
The 4D gravitational model with a real scalar field (varphi), Einstein and Gauss–Bonnet terms is considered. The action contains the potential (U(varphi)) and the Gauss–Bonnet coupling function (f(varphi)). For a special static spherically symmetric metric (ds^{2}=(A(u))^{-1}du^{2}-A(u)dt^{2}+u^{2}dOmega^{2}), with (A(u)>0) ((u>0) is a radial coordinate), we verify the so-called reconstruction procedure suggested by Nojiri and Nashed. This procedure presents certain implicit relations for (U(varphi)) and (f(varphi)) which lead to exact solutions to the equations of motion for a given metric governed by (A(u)). We confirm that all relations in the approach of Nojiri and Nashed for (f(varphi(u))) and (varphi(u)) are correct, but the relation for (U(varphi(u))) contains a typo which is eliminated in this paper. Here we apply the procedure to the (external) Schwarzschild metric with the gravitational radius (2mu) and (u>2mu). Using the “no-ghost” restriction (i.e., reality of (varphi(u))), we find two families of ((U(varphi),f(varphi))). The first one gives us the Schwarzschild metric defined for (u>3mu), while the second one describes the Schwarzschild metric defined for (2mu<u<3mu) ((3mu) is the radius of the photon sphere). In both cases the potential (U(varphi)) is negative.
Abstract The 4D gravitational model with a real scalar field (varphi), Einstein and Gauss-Bonnet terms is considered.作用包含势（U(varphi)）和高斯-波奈耦合函数（f(varphi)）。对于特殊的静态球对称度量 (ds^{2}=(A(u))^{-1}du^{2}-A(u)dt^{2}+u^{2}dOmega^{2}（(A(u)>0）（(u>0）是一个径向坐标），我们验证了 Nojiri 和 Nashed 提出的所谓重构过程。这个过程为(U(varphi))和(f(varphi))提出了某些隐含关系，这些关系导致了受(A(u))支配的给定度量的运动方程的精确解。我们确认野尻和纳希什的方法中关于 (f(varphi(u))) 和 (varphi(u)) 的所有关系都是正确的，但关于 (U(varphi(u))) 的关系包含一个错字，本文将其删除。在这里，我们将这一过程应用于（外部）施瓦兹柴尔德度量，其引力半径为(2mu)和(u>2mu)。使用 "无鬼 "限制（即 (varphi(u))的现实性），我们找到了两个系列的 ((U(varphi),f(varphi))。第一个族给出了定义为（u>3mu）的施瓦兹柴尔德度量，而第二个族描述了定义为（2mu<u<3mu）的施瓦兹柴尔德度量（（3mu）是光子球的半径）。在这两种情况下势能都是负的
{"title":"On a Reconstruction Procedure for Special Spherically Symmetric Metrics in the Scalar-Einstein–Gauss–Bonnet Model: the Schwarzschild Metric Test","authors":"K. K. Ernazarov, V. D. Ivashchuk","doi":"10.1134/s0202289324700257","DOIUrl":"https://doi.org/10.1134/s0202289324700257","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>The 4D gravitational model with a real scalar field <span>(varphi)</span>, Einstein and Gauss–Bonnet terms is considered. The action contains the potential <span>(U(varphi))</span> and the Gauss–Bonnet coupling function <span>(f(varphi))</span>. For a special static spherically symmetric metric <span>(ds^{2}=(A(u))^{-1}du^{2}-A(u)dt^{2}+u^{2}dOmega^{2})</span>, with <span>(A(u)>0)</span> (<span>(u>0)</span> is a radial coordinate), we verify the so-called reconstruction procedure suggested by Nojiri and Nashed. This procedure presents certain implicit relations for <span>(U(varphi))</span> and <span>(f(varphi))</span> which lead to exact solutions to the equations of motion for a given metric governed by <span>(A(u))</span>. We confirm that all relations in the approach of Nojiri and Nashed for <span>(f(varphi(u)))</span> and <span>(varphi(u))</span> are correct, but the relation for <span>(U(varphi(u)))</span> contains a typo which is eliminated in this paper. Here we apply the procedure to the (external) Schwarzschild metric with the gravitational radius <span>(2mu)</span> and <span>(u>2mu)</span>. Using the “no-ghost” restriction (i.e., reality of <span>(varphi(u))</span>), we find two families of <span>((U(varphi),f(varphi)))</span>. The first one gives us the Schwarzschild metric defined for <span>(u>3mu)</span>, while the second one describes the Schwarzschild metric defined for <span>(2mu<u<3mu)</span> (<span>(3mu)</span> is the radius of the photon sphere). In both cases the potential <span>(U(varphi))</span> is negative.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209695","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-08-23DOI: 10.1134/s0202289324700233
Isaac Lobo, Allan Ernest, Matthew Collins
Abstract
Gravitational quantum theory applied to the weak gravity regions of deep gravitational wells predicts that photon-particle interaction cross sections can vary significantly, depending on the eigenspectral composition of the particle’s wave function. These often-reduced cross sections can potentially enable the nature and origin of dark matter to be understood without recourse to new particles or new physics, and without compromising the observations from nucleosynthesis and the cosmic microwave background. The present work extends the calculations of the Einstein-(A) coefficients relevant to these photon interactions (previously carried out for (1/r) central point-mass (CPM) potentials) to potentials derived from Navarro–Frenk–White (NFW) radial density profiles, which more realistically describe galaxy halos. The Wentzel–Kramers–Brillouin (WKB) and Modified Airy Function (MAF) approximation strategies were used to find the eigenfunctions appropriate to these potentials, and hence obtain the relevant Einstein-(A) coefficients. The results show that states with high principal and angular quantum number in NFW potentials have a significantly low transition rate. The results are also compared to those in the CPM potentials published in an earlier work.
{"title":"Quantum Gravitational Eigenstates in Navarro–Frenk–White Potentials","authors":"Isaac Lobo, Allan Ernest, Matthew Collins","doi":"10.1134/s0202289324700233","DOIUrl":"https://doi.org/10.1134/s0202289324700233","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p>Gravitational quantum theory applied to the weak gravity regions of deep gravitational wells predicts that photon-particle interaction cross sections can vary significantly, depending on the eigenspectral composition of the particle’s wave function. These often-reduced cross sections can potentially enable the nature and origin of dark matter to be understood without recourse to new particles or new physics, and without compromising the observations from nucleosynthesis and the cosmic microwave background. The present work extends the calculations of the Einstein-<span>(A)</span> coefficients relevant to these photon interactions (previously carried out for <span>(1/r)</span> central point-mass (CPM) potentials) to potentials derived from Navarro–Frenk–White (NFW) radial density profiles, which more realistically describe galaxy halos. The Wentzel–Kramers–Brillouin (WKB) and Modified Airy Function (MAF) approximation strategies were used to find the eigenfunctions appropriate to these potentials, and hence obtain the relevant Einstein-<span>(A)</span> coefficients. The results show that states with high principal and angular quantum number in NFW potentials have a significantly low transition rate. The results are also compared to those in the CPM potentials published in an earlier work.</p>","PeriodicalId":583,"journal":{"name":"Gravitation and Cosmology","volume":null,"pages":null},"PeriodicalIF":1.173,"publicationDate":"2024-08-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142209693","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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