Pub Date : 2024-05-30DOI: 10.1088/1361-6382/ad4dff
Fawzi Aly and Dejan Stojkovic
The Kruskal–Szekeres coordinate construction for the Schwarzschild spacetime could be interpreted simply as a squeezing of the t-line into a single point, at the event horizon . Starting from this perspective, we extend the Kruskal charting to spacetimes with two horizons, in particular the Reissner–Nordström manifold, . We develop a new method to construct Kruskal-like coordinates through casting the metric in new null coordinates, and find two algebraically distinct ways to chart , referred to as classes: type-I and type-II within this work. We pedagogically illustrate our method by crafting two compact, conformal, and global coordinate systems labeled and as an example for each class respectively, and plot the corresponding Penrose diagrams. In both coordinates, the metric differentiability can be promoted to in a straightforward way. Finally, the conformal metric factor can be written explicitly in terms of the t and r functions for both types of charts. We also argued that the chart recently reported in Soltani (2023 arXiv:2307.11026) could be viewed as another example for the type-II classification, similar to .
施瓦兹柴尔德时空的 Kruskal-Szekeres 坐标构造可以简单地解释为在事件视界处将 t 线挤压成一个点。从这个角度出发，我们将克鲁斯卡尔制图扩展到具有两个视界的时空，特别是赖斯纳-诺德斯特伦流形。 我们开发了一种新方法，通过在新的空坐标中铸造度量来构建类似克鲁斯卡尔的坐标，并找到了两种代数上截然不同的制图方法，在本文中被称为类：I型和II型。我们通过制作两个紧凑、保形和全局坐标系，分别标注为和，作为每类坐标系的示例，并绘制相应的彭罗斯图，从教学角度说明了我们的方法。在这两个坐标系中，度量可微分性都可以直接提升到。最后，对于这两类图表，共形度量因子都可以用 t 和 r 函数明确地写出。我们还认为，索尔塔尼（2023 arXiv:2307.11026）最近报告的图表可以看作是第二类分类的另一个例子，类似于......。
{"title":"On the generalization of the Kruskal–Szekeres coordinates: a global conformal charting of the Reissner–Nordström spacetime","authors":"Fawzi Aly and Dejan Stojkovic","doi":"10.1088/1361-6382/ad4dff","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4dff","url":null,"abstract":"The Kruskal–Szekeres coordinate construction for the Schwarzschild spacetime could be interpreted simply as a squeezing of the t-line into a single point, at the event horizon . Starting from this perspective, we extend the Kruskal charting to spacetimes with two horizons, in particular the Reissner–Nordström manifold, . We develop a new method to construct Kruskal-like coordinates through casting the metric in new null coordinates, and find two algebraically distinct ways to chart , referred to as classes: type-I and type-II within this work. We pedagogically illustrate our method by crafting two compact, conformal, and global coordinate systems labeled and as an example for each class respectively, and plot the corresponding Penrose diagrams. In both coordinates, the metric differentiability can be promoted to in a straightforward way. Finally, the conformal metric factor can be written explicitly in terms of the t and r functions for both types of charts. We also argued that the chart recently reported in Soltani (2023 arXiv:2307.11026) could be viewed as another example for the type-II classification, similar to .","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141182846","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-27DOI: 10.1088/1361-6382/ad4ae3
Rituparna Mandal and Soma Sanyal
We investigate the quantum modified cosmological dynamical equations in a Friedmann–Lemaître–Robertson–Walker universe filled with a barotropic fluid and a general non-canonical scalar field characterized by a Lagrangian similar to k-essence model but with a potential term. Quantum corrections are incorporated by considering the running of the gravitational and potential couplings, employing the functional renormalization group approach. Covariant conservation of the non-canonical scalar field and the background barotropic fluid is considered separately, imposing a constraint resulting from the Bianchi identity. This constraint determines the evolution of the cut-off scale with the scale factor and also reveals the cosmic fixed points, depending on whether the flow ceases or continues to evolve. We explore how the general non-canonical scalar field parameter affects the different types of cosmic fixed points and how it differs from the canonical case. Furthermore, we establish a bound on the ratio of the renormalization group parameters involving the non-canonical parameter for which the universe may exhibit accelerated expansion for mixed fixed points. This bound indicates the non-canonical scalar field includes larger sets of asymptotically safe renormalization group fixed point which may give rise to an accelerated universe.
{"title":"Asymptotically safe cosmology with non-canonical scalar field","authors":"Rituparna Mandal and Soma Sanyal","doi":"10.1088/1361-6382/ad4ae3","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4ae3","url":null,"abstract":"We investigate the quantum modified cosmological dynamical equations in a Friedmann–Lemaître–Robertson–Walker universe filled with a barotropic fluid and a general non-canonical scalar field characterized by a Lagrangian similar to k-essence model but with a potential term. Quantum corrections are incorporated by considering the running of the gravitational and potential couplings, employing the functional renormalization group approach. Covariant conservation of the non-canonical scalar field and the background barotropic fluid is considered separately, imposing a constraint resulting from the Bianchi identity. This constraint determines the evolution of the cut-off scale with the scale factor and also reveals the cosmic fixed points, depending on whether the flow ceases or continues to evolve. We explore how the general non-canonical scalar field parameter affects the different types of cosmic fixed points and how it differs from the canonical case. Furthermore, we establish a bound on the ratio of the renormalization group parameters involving the non-canonical parameter for which the universe may exhibit accelerated expansion for mixed fixed points. This bound indicates the non-canonical scalar field includes larger sets of asymptotically safe renormalization group fixed point which may give rise to an accelerated universe.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141159635","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-23DOI: 10.1088/1361-6382/ad4fda
Abhishek Kumar Mehta
In this paper, Dirac Quantization of $3D$ gravity in the first-order formalism is attempted where instead of quantizing the connection and triad fields, the connection and the triad 1-forms themselves are quantized. The exterior derivative operator on the space of differential forms is treated as the `time' derivative to compute the momenta conjugate to these 1-forms. This manner of quantization allows one to compute the transition amplitude in $3D$ gravity which has a close, but not exact, match with the transition amplitude computed via LQG techniques. This inconsistency is interpreted as being due to the non-quantizable nature of differential geometry.
{"title":"Necessity of quantizable geometry for quantum gravity","authors":"Abhishek Kumar Mehta","doi":"10.1088/1361-6382/ad4fda","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4fda","url":null,"abstract":"\u0000 In this paper, Dirac Quantization of $3D$ gravity in the first-order formalism is attempted where instead of quantizing the connection and triad fields, the connection and the triad 1-forms themselves are quantized. The exterior derivative operator on the space of differential forms is treated as the `time' derivative to compute the momenta conjugate to these 1-forms. This manner of quantization allows one to compute the transition amplitude in $3D$ gravity which has a close, but not exact, match with the transition amplitude computed via LQG techniques. This inconsistency is interpreted as being due to the non-quantizable nature of differential geometry.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141103677","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-23DOI: 10.1088/1361-6382/ad4ae4
Orlando Luongo and Hernando Quevedo
We evaluate the effects of repulsive gravity using first order geometric invariants, i.e. the Ricci scalar and the eigenvalues of the Riemann curvature tensor, for three regular black holes, namely the Bardeen, Hayward, and Dymnikova spacetimes. To examine the repulsive effects, we calculate their respective onsets and regions of repulsive gravity. Afterwards, we compare the repulsive regions obtained from these metrics among themselves and then with the predictions got from the Reissner–Nordström and Schwarzschild–de Sitter. A notable characteristic, observed in all these metrics, is that the repulsive regions appear to be unaffected by the mass that generates the regular black hole. This property emerges due to the invariants employed in our analysis, which do not change sign through linear combinations of the mass and the free coefficients of the metrics. As a result, gravity can change sign independently of the specific values acquired by the mass. This conclusion suggests a potential incompleteness of regular solutions, particularly in terms of their repulsive effects. To further highlight this finding, we numerically compute, for the Reissner–Nordström and Schwarzschild–de Sitter solutions, the values of mass, M, that emulate the repulsive effects found in the Bardeen and Hayward spacetimes. These selected values of M provide evidence that regular black holes do not incorporate repulsive effects by means of the masses used to generate the solutions themselves. Implications and physical consequences of these results are then discussed in detail.
我们利用一阶几何不变量，即里奇标量和黎曼曲率张量的特征值，评估了三种规则黑洞，即巴丁、海沃德和迪姆尼科娃时空的斥引力效应。为了检验斥力效应，我们计算了它们各自的起始点和斥力引力区域。之后，我们将这些度量得到的斥引力区域相互比较，然后与赖斯纳-诺德斯特伦和施瓦兹希尔德-德-西特的预测进行比较。在所有这些度量中观察到的一个显著特点是，斥力区域似乎不受产生规则黑洞的质量的影响。这一特性的出现得益于我们在分析中使用的不变式，它不会因为质量和度量的自由系数的线性组合而改变符号。因此，引力的符号变化与质量的具体数值无关。这一结论表明，正则解可能并不完整，尤其是在其排斥效应方面。为了进一步强调这一发现，我们对赖斯纳-诺德斯特伦和施瓦兹希尔德-德-西特解进行了数值计算，得出了模仿巴丁和海沃德时空中的斥力效应的质量值 M。这些选定的 M 值提供了证据，证明常规黑洞不会通过用于生成解本身的质量而产生斥力效应。接下来将详细讨论这些结果的含义和物理后果。
{"title":"Repulsive gravity in regular black holes","authors":"Orlando Luongo and Hernando Quevedo","doi":"10.1088/1361-6382/ad4ae4","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4ae4","url":null,"abstract":"We evaluate the effects of repulsive gravity using first order geometric invariants, i.e. the Ricci scalar and the eigenvalues of the Riemann curvature tensor, for three regular black holes, namely the Bardeen, Hayward, and Dymnikova spacetimes. To examine the repulsive effects, we calculate their respective onsets and regions of repulsive gravity. Afterwards, we compare the repulsive regions obtained from these metrics among themselves and then with the predictions got from the Reissner–Nordström and Schwarzschild–de Sitter. A notable characteristic, observed in all these metrics, is that the repulsive regions appear to be unaffected by the mass that generates the regular black hole. This property emerges due to the invariants employed in our analysis, which do not change sign through linear combinations of the mass and the free coefficients of the metrics. As a result, gravity can change sign independently of the specific values acquired by the mass. This conclusion suggests a potential incompleteness of regular solutions, particularly in terms of their repulsive effects. To further highlight this finding, we numerically compute, for the Reissner–Nordström and Schwarzschild–de Sitter solutions, the values of mass, M, that emulate the repulsive effects found in the Bardeen and Hayward spacetimes. These selected values of M provide evidence that regular black holes do not incorporate repulsive effects by means of the masses used to generate the solutions themselves. Implications and physical consequences of these results are then discussed in detail.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141092009","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-22DOI: 10.1088/1361-6382/ad4a1a
András László and Zsigmond Tarcsay
In nonperturbative formulation of quantum field theory, the vacuum state is characterized by the Wilsonian renormalization group (RG) flow of Feynman type field correlators. Such a flow is a parametric family of ultraviolet (UV) regularized field correlators, the parameter being the strength of the UV regularization, and the instances with different strength of UV regularizations are linked by the renormalization group equation. Important RG flows are those which reach out to any UV regularization strengths. In this paper it is shown that for these flows a natural, mathematically rigorous generally covariant definition can be given, and that they form a topological vector space which is Hausdorff, locally convex, complete, nuclear, semi-Montel, Schwartz. That is, they form a generalized function space having favorable properties, similar to multivariate distributions. The other theorem proved in the paper is that for Wilsonian RG flows reaching out to all UV regularization strengths, a simple factorization formula holds in case of bosonic fields over flat (affine) spacetime: the flow always originates from a regularization-independent distributional correlator, and its running satisfies an algebraic ansatz. The conjecture is that this factorization theorem should generically hold, which is worth future investigations.
{"title":"On the running and the UV limit of Wilsonian renormalization group flows","authors":"András László and Zsigmond Tarcsay","doi":"10.1088/1361-6382/ad4a1a","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4a1a","url":null,"abstract":"In nonperturbative formulation of quantum field theory, the vacuum state is characterized by the Wilsonian renormalization group (RG) flow of Feynman type field correlators. Such a flow is a parametric family of ultraviolet (UV) regularized field correlators, the parameter being the strength of the UV regularization, and the instances with different strength of UV regularizations are linked by the renormalization group equation. Important RG flows are those which reach out to any UV regularization strengths. In this paper it is shown that for these flows a natural, mathematically rigorous generally covariant definition can be given, and that they form a topological vector space which is Hausdorff, locally convex, complete, nuclear, semi-Montel, Schwartz. That is, they form a generalized function space having favorable properties, similar to multivariate distributions. The other theorem proved in the paper is that for Wilsonian RG flows reaching out to all UV regularization strengths, a simple factorization formula holds in case of bosonic fields over flat (affine) spacetime: the flow always originates from a regularization-independent distributional correlator, and its running satisfies an algebraic ansatz. The conjecture is that this factorization theorem should generically hold, which is worth future investigations.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141085360","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-22DOI: 10.1088/1361-6382/ad4506
Ilkka Mäkinen
We introduce a master constraint operator on the kinematical Hilbert space of loop quantum gravity representing a set of gauge conditions which classically fix the densitized triad to be diagonal. We argue that the master constraint approach provides a natural and systematic way of carrying out the quantum gauge-fixing procedure which underlies the model known as quantum-reduced loop gravity. The Hilbert space of quantum-reduced loop gravity is obtained as a particular space of solutions of the gauge-fixing master constraint operator. We give a concise summary of the fundamental structure of the quantum-reduced framework, and consider several possible extensions thereof, for which the master constraint formulation provides a convenient starting point. In particular, we propose a generalization of the standard Hilbert space of quantum-reduced loop gravity, which may be relevant in the application of the quantum-reduced model to physical situations in which the Ashtekar connection is not diagonal.
{"title":"Master constraint approach to quantum-reduced loop gravity","authors":"Ilkka Mäkinen","doi":"10.1088/1361-6382/ad4506","DOIUrl":"https://doi.org/10.1088/1361-6382/ad4506","url":null,"abstract":"We introduce a master constraint operator on the kinematical Hilbert space of loop quantum gravity representing a set of gauge conditions which classically fix the densitized triad to be diagonal. We argue that the master constraint approach provides a natural and systematic way of carrying out the quantum gauge-fixing procedure which underlies the model known as quantum-reduced loop gravity. The Hilbert space of quantum-reduced loop gravity is obtained as a particular space of solutions of the gauge-fixing master constraint operator. We give a concise summary of the fundamental structure of the quantum-reduced framework, and consider several possible extensions thereof, for which the master constraint formulation provides a convenient starting point. In particular, we propose a generalization of the standard Hilbert space of quantum-reduced loop gravity, which may be relevant in the application of the quantum-reduced model to physical situations in which the Ashtekar connection is not diagonal.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141085580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-22DOI: 10.1088/1361-6382/ad494c
Samarjit Chakraborty, Sunil D Maharaj, Sarbari Guha and Rituparno Goswami
We investigate the status of the gravitational arrow of time in the case of a spherical collapse of a fluid that conducts heat and radiates energy. In particular, we examine the results obtained by W. B. Bonnor in his 1985 paper where he found that the gravitational arrow of time was opposite to the thermodynamic arrow of time. The measure of gravitational epoch function P used by Bonnor was given by the ratio of the Weyl square to the Ricci square. In this paper, we have assumed the measure of gravitational entropy (GE) P1 to be given by the ratio of the Weyl scalar to the Kretschmann scalar. Our analysis indicates that Bonnor’s result seems to be validated, i.e. the gravitational arrow and the thermodynamic arrow of time point in opposite directions. This strengthens the opinion that the Weyl proposal of GE applies only to the Universe as a whole (provided that we exclude the white holes).
我们研究了导热和辐射能量的流体的球形坍缩情况下时间引力箭头的状况。我们特别研究了 W. B. Bonnor 在其 1985 年论文中获得的结果，他发现引力时间箭头与热力学时间箭头相反。波纳尔使用的引力纪元函数 P 的度量是由韦尔平方与利玛窦平方之比给出的。在本文中，我们假定引力熵（GE）的度量 P1 是由韦尔标量与克雷奇曼标量之比给出的。我们的分析表明，波诺的结果似乎得到了验证，即时间的引力箭头和热力学箭头指向相反的方向。这加强了我们的观点，即韦尔提出的GE只适用于整个宇宙（前提是我们排除白洞）。
{"title":"Arrow of time and gravitational entropy in collapse","authors":"Samarjit Chakraborty, Sunil D Maharaj, Sarbari Guha and Rituparno Goswami","doi":"10.1088/1361-6382/ad494c","DOIUrl":"https://doi.org/10.1088/1361-6382/ad494c","url":null,"abstract":"We investigate the status of the gravitational arrow of time in the case of a spherical collapse of a fluid that conducts heat and radiates energy. In particular, we examine the results obtained by W. B. Bonnor in his 1985 paper where he found that the gravitational arrow of time was opposite to the thermodynamic arrow of time. The measure of gravitational epoch function P used by Bonnor was given by the ratio of the Weyl square to the Ricci square. In this paper, we have assumed the measure of gravitational entropy (GE) P1 to be given by the ratio of the Weyl scalar to the Kretschmann scalar. Our analysis indicates that Bonnor’s result seems to be validated, i.e. the gravitational arrow and the thermodynamic arrow of time point in opposite directions. This strengthens the opinion that the Weyl proposal of GE applies only to the Universe as a whole (provided that we exclude the white holes).","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141085402","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-21DOI: 10.1088/1361-6382/ad494b
Anand Balivada, Pius Ranjan Padhi and Amitabh Virmani
In a recent paper (Kim et al 2023 arXiv:2305.08922 [hep-th]), it has been proposed that the endpoint of the Kerr-AdS superradiant instability is a Grey Galaxy. The conjectured solutions are supposed to be made up of a black hole with critical angular velocity in the centre of AdS, surrounded by a large flat disk of thermal bulk gas that revolves around the black hole. In the analysis of the proposed solutions so far, gravitational effects due to the black hole on the thermal gas have been neglected. A way to estimate these effects is via computing tidal forces. With this motivation, we study tidal forces on objects moving in the Kerr-AdS spacetime. To do so, we construct a parallel-transported orthonormal frame along an arbitrary timelike or null geodesic. We then specialise to the class of fast rotating geodesics lying in the equatorial plane, and estimate tidal forces on the gas in the Grey galaxies, modelling it as a collection of particles moving on timelike geodesics. We show that the tidal forces are small (and remain small even in the large mass limit), thereby providing additional support to the idea that the gas is weakly interacting with the black hole.
最近的一篇论文（Kim et al 2023 arXiv:2305.08922 [hep-th]）提出，克尔-AdS超辐射不稳定性的终点是灰色星系。猜想中的解决方案应该是由一个位于 AdS 中心、具有临界角速度的黑洞组成，黑洞周围是一个围绕黑洞旋转的大型扁平热气体盘。在迄今为止对所提方案的分析中，黑洞对热气体的引力效应被忽略了。估算这些效应的一种方法是计算潮汐力。基于这一动机，我们研究了在克尔-AdS 时空中运动的物体所受的潮汐力。为此，我们沿着任意时间线或空大地线构建了一个平行移动的正交帧。然后，我们专门研究了位于赤道面上的快速旋转测地线类别，并估算了格雷星系中气体的潮汐力，将其模拟为在时间测地线上运动的粒子集合。我们的研究表明，潮汐力很小（即使在大质量极限时也仍然很小），从而为气体与黑洞的弱相互作用这一观点提供了额外的支持。
{"title":"Tidal forces in Kerr-AdS and Grey galaxies","authors":"Anand Balivada, Pius Ranjan Padhi and Amitabh Virmani","doi":"10.1088/1361-6382/ad494b","DOIUrl":"https://doi.org/10.1088/1361-6382/ad494b","url":null,"abstract":"In a recent paper (Kim et al 2023 arXiv:2305.08922 [hep-th]), it has been proposed that the endpoint of the Kerr-AdS superradiant instability is a Grey Galaxy. The conjectured solutions are supposed to be made up of a black hole with critical angular velocity in the centre of AdS, surrounded by a large flat disk of thermal bulk gas that revolves around the black hole. In the analysis of the proposed solutions so far, gravitational effects due to the black hole on the thermal gas have been neglected. A way to estimate these effects is via computing tidal forces. With this motivation, we study tidal forces on objects moving in the Kerr-AdS spacetime. To do so, we construct a parallel-transported orthonormal frame along an arbitrary timelike or null geodesic. We then specialise to the class of fast rotating geodesics lying in the equatorial plane, and estimate tidal forces on the gas in the Grey galaxies, modelling it as a collection of particles moving on timelike geodesics. We show that the tidal forces are small (and remain small even in the large mass limit), thereby providing additional support to the idea that the gas is weakly interacting with the black hole.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141079030","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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 : 2024-05-16DOI: 10.1088/1361-6382/ad43a9
Roberto Giambò and Orlando Luongo
We examine a spherically-symmetric class of spacetimes carrying vacuum energy, while considering the influence of an external dark energy environment represented by a non-dynamical quintessence field. Our investigation focuses on a specific set of solutions affected by this field, leading to distinct kinds of spacetime deformations, resulting in regular, singular, and wormhole solutions. We thoroughly discuss the underlying physics associated with each case and demonstrate that more complex deformations are prone to instability. Ultimately, we find that our results lead to an isotropic de Sitter-like solution that behaves as a quintessence fluid. To achieve this, we investigate the nature of the corresponding fluid, showing that it cannot provide the sound speed equal to a constant equation of state parameter near the center. Consequently, we reinterpret the fluid as a slow-roll quintessence by investigating its behavior in asymptotic regimes. Further, we explore the potential implications of violating the isotropy condition on the pressures and we finally compare our findings with the de Sitter and Hayward solutions, highlighting both the advantages and disadvantages of our scenarios.
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Pub Date : 2024-05-15DOI: 10.1088/1361-6382/ad46c0
Johanna N Borissova
We investigate the requirement of suppressing spacetime geometries with a curvature singularity via destructive interference in the Lorentzian gravitational path integral as a constraint on the microscopic action for gravity. Based on simple examples of static spherically symmetric spacetimes, we demonstrate that complete singularity suppression in the path integral stipulates that the action for gravity be of infinite order in the curvature.
{"title":"Suppression of spacetime singularities in quantum gravity","authors":"Johanna N Borissova","doi":"10.1088/1361-6382/ad46c0","DOIUrl":"https://doi.org/10.1088/1361-6382/ad46c0","url":null,"abstract":"We investigate the requirement of suppressing spacetime geometries with a curvature singularity via destructive interference in the Lorentzian gravitational path integral as a constraint on the microscopic action for gravity. Based on simple examples of static spherically symmetric spacetimes, we demonstrate that complete singularity suppression in the path integral stipulates that the action for gravity be of infinite order in the curvature.","PeriodicalId":10282,"journal":{"name":"Classical and Quantum Gravity","volume":null,"pages":null},"PeriodicalIF":3.5,"publicationDate":"2024-05-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140949521","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"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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