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Relativistic fluids in cosmological spacetimes 宇宙学时空中的相对论流体
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-29 DOI: 10.1088/1361-6382/ad84ad
David Fajman, Maximilian Ofner and Zoe Wyatt
We review the status of mathematical research on the dynamical properties of relativistic fluids in cosmological spacetimes–both, in the presence of gravitational backreaction as well as the evolution on fixed cosmological backgrounds. We focus in particular on the phenomenon of fluid stabilization, which describes the taming effect of spacetime expansion on the fluid. While fluids are in general known to form shocks from regular initial data, spacetime expansion has been found to suppress this behaviour. During the last decade, various rigorous results on this problem have been put forward. We review these results, the mathematical methods involved and provide an outlook on open questions.
我们回顾了宇宙学时空中相对论流体动力学特性的数学研究现状--既包括引力反作用的存在,也包括固定宇宙学背景下的演化。我们特别关注流体稳定现象,它描述了时空膨胀对流体的驯服效应。众所周知,流体一般会从规则的初始数据中形成冲击,但人们发现时空膨胀会抑制这种行为。在过去的十年中,关于这个问题的各种严谨结果被提出来。我们回顾了这些结果、所涉及的数学方法,并对悬而未决的问题进行了展望。
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引用次数: 0
The Virgo Newtonian calibration system for the O4 observing run 用于 O4 观测运行的处女座牛顿式校准系统
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-29 DOI: 10.1088/1361-6382/ad869c
F Aubin, E Dangelser, D Estevez, A Masserot, B Mours, T Pradier, A Syx and P Van Hove
After initial tests performed during previous observing runs, a Newtonian calibrator (NCal) system was developed and installed on the Virgo gravitational wave detector for the O4 observing run. This system, which is continuously operated, provides the absolute calibration of Virgo for this run. Its uncertainty of 0.17% on the amplitudes of the injected signals is better than that obtained with other calibration techniques like the photon calibrator (PCal). This paper presents this NCal system and details the different sources of uncertainties.
在前几次观测运行期间进行了初步测试之后,开发了牛顿校准器(NCal)系统,并安装在室女座引力波探测器上,用于 O4 观测运行。该系统持续运行,为本次运行提供室女座绝对校准。其注入信号振幅的不确定性为 0.17%,优于光子校准器(PCal)等其他校准技术。本文介绍了这一 NCal 系统,并详细说明了不确定性的不同来源。
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引用次数: 0
Mass octupole and current quadrupole corrections to gravitational wave emission from close hyperbolic encounters 近距离双曲面相遇引力波发射的质量八极和电流四极校正
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-24 DOI: 10.1088/1361-6382/ad869a
Alexander Roskill, Marienza Caldarola, Sachiko Kuroyanagi and Savvas Nesseris
In this paper, we study the next-to-leading order corrections in the mass multipole expansion, i.e. the mass octupole and current quadrupole, to gravitational wave production by close hyperbolic encounters of compact objects. We find that the signal is again, as in the simple quadrupole case, a burst event with the majority of the released energy occurring during the closest approach. In particular, we investigate the relative contribution to the power, both in the time and frequency domains, and total energy emitted by each order in the mass multipole expansion in gravitational waves. To do so, we include in the quadrupole term its first order post-Newtonian correction, giving this a contribution to the power of the same order as that of the mass octupole and the current quadrupole. We find specific configurations of systems where these corrections could be important and should be taken into account when analysing burst events.
在本文中,我们研究了质量多极扩展中的次引阶修正,即质量八极和电流四极,对紧凑天体近距离双曲相遇产生的引力波的修正。我们发现,与简单的四极情况一样,该信号也是一个爆发事件,大部分释放的能量发生在最接近期间。我们特别研究了引力波质量多极扩展中每一阶在时域和频域对功率的相对贡献以及发射的总能量。为此,我们在四极子项中加入了一阶牛顿后修正,使其对功率的贡献与质量八极子和电流四极子的贡献同阶。我们发现,在一些特定的系统配置中,这些修正可能非常重要,在分析爆发事件时应该加以考虑。
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引用次数: 0
Deflection of light by wormholes and its shadow due to dark matter within modified symmetric teleparallel gravity formalism 虫洞对光线的偏转以及修正对称远距离平行引力形式主义中暗物质造成的光线阴影
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-24 DOI: 10.1088/1361-6382/ad869d
G Mustafa, Zinnat Hassan and P K Sahoo
We explore the possibility of traversable wormhole formation in the dark matter halos in the context of f(Q) gravity. We obtain the exact wormhole solutions with anisotropic matter source based on the Bose–Einstein condensate, Navarro-Frenk-White, and pseudo-isothermal matter density profiles. Notably, we present a novel wormhole solution supported by these dark matters using the expressions for the density profile and rotational velocity along with the modified field equations to calculate the redshift and shape functions of the wormholes. With a particular set of parameters, we demonstrate that our proposed wormhole solutions fulfill the flare-out condition against an asymptotic background. Additionally, we examine the energy conditions (ECs), focusing on the null ECs at the wormhole’s throat, providing a graphical representation of the feasible and negative regions. Our study also examines the wormhole’s shadow in the presence of various dark matter models, revealing that higher central densities result in a shadow closer to the throat, whereas lower values have the opposite effect. Moreover, we explore the deflection of light when it encounters these wormholes, particularly noting that light deflection approaches infinity at the throat, where the gravitational field is extremely strong.
我们探索了在 f(Q) 引力背景下暗物质晕中形成可穿越虫洞的可能性。我们根据玻色-爱因斯坦凝聚态、纳瓦罗-弗伦克-怀特和伪等温物质密度曲线,得到了各向异性物质源的精确虫洞方案。值得注意的是,我们提出了一种由这些暗物质支持的新型虫洞方案,利用密度剖面和旋转速度的表达式以及修正的场方程来计算虫洞的红移和形状函数。通过一组特定的参数,我们证明了我们提出的虫洞方案满足渐近背景下的耀斑条件。此外,我们还研究了能量条件(ECs),重点是虫洞咽喉处的空ECs,并提供了可行区域和负区域的图示。我们的研究还检验了各种暗物质模型下的虫洞阴影,发现较高的中心密度会导致阴影更靠近虫洞喉部,而较低的中心密度则会产生相反的效果。此外,我们还探讨了光在遇到这些虫洞时的偏转,尤其注意到在引力场极强的咽喉处,光的偏转接近无穷大。
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引用次数: 0
Efficient Bayesian inference and model selection for continuous gravitational waves in pulsar timing array data 脉冲星定时阵列数据中连续引力波的高效贝叶斯推理和模型选择
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-22 DOI: 10.1088/1361-6382/ad84b0
Bence Bécsy
Finding and characterizing gravitational waves from individual supermassive black hole binaries is a central goal of pulsar timing array experiments, which will require analysis methods that can be efficient on our rapidly growing datasets. Here we present a novel approach built on three key elements: (i) precalculating and interpolating expensive matrix operations; (ii) semi-analytically marginalizing over the gravitational-wave phase at the pulsars; (iii) numerically marginalizing over the pulsar distance uncertainties. With these improvements the recent NANOGrav 15 yr dataset can be analyzed in minutes after an setup phase, instead of an analysis taking days–weeks with previous methods. The same setup can be used to efficiently analyze the dataset under any sinusoidal deterministic model. In particular, this will aid testing the binary hypothesis by allowing for efficient analysis of competing models (e.g. incoherent, monopolar, or dipolar sine wave model) and scrambled datasets for false alarm studies. The same setup can be updated in minutes for new realizations of the data, which enables large simulation studies.
寻找和描述来自单个超大质量黑洞双星的引力波是脉冲星定时阵列实验的一个核心目标,这就要求分析方法能够有效地处理我们快速增长的数据集。在此,我们提出一种基于三个关键要素的新方法:(i) 对昂贵的矩阵运算进行预计算和插值;(ii) 对脉冲星的引力波相位进行半分析式边际化;(iii) 对脉冲星距离的不确定性进行数值边际化。通过这些改进,最近的 NANOGrav 15 年数据集可在设置阶段后几分钟内完成分析,而以前的方法则需要几天到几周的时间。同样的设置可用于在任何正弦确定性模型下高效分析数据集。特别是,这将有助于测试二元假说,可以高效分析竞争模型(如不连贯、单极性或双极性正弦波模型)和用于误报研究的扰乱数据集。同样的设置可在几分钟内根据新的数据实现情况进行更新,从而实现大型模拟研究。
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引用次数: 0
Non-linear charged dS spacetime and its thermodynamics and Schottky Anomaly 非线性带电 dS 时空及其热力学和肖特基反常现象
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-22 DOI: 10.1088/1361-6382/ad828e
Hai-Long Zhen, Yun-Zhi Du, Huai-Fan Li, Li-Chun Zhang and Yu-Bo Ma
In this paper, firstly, the conditions and existence region for the coexistence of the black hole and cosmological horizons in Non-linear charged dS (NLC-dS) spacetime are discussed, subsequently, the thermodynamic quantities for which the boundary conditions are satisfied in spacetime in the coexistence region of the two horizons are discussed, and the effective thermodynamic quantities in the NLC-dS spacetime in the coexistence region with two horizons are presented. Based on these, the heat capacity in the coexistence region with two horizons is addressed, the behavior of the heat capacity in the NLC-dS spacetime in the aforementioned region is found to exhibit the characteristics of Schottky specific heat. In order to investigate the intrinsic reason of the heat capacity in spacetime, we regard the two horizons in the NLC-dS spacetime as two distinct energy levels, consequently, the microscopic particles at different horizons exhibit disparate energies. Using the heat capacity relationship between the two-energy levels in an ordinary thermodynamic system, the heat capacity in dS spacetime is discussed, it is observed that the behavior of the heat capacity is analogous to that of the two-energy levels in an ordinary thermodynamic system. The number of microscopic particles in the two-energy-level system are approximated by comparing the maximum value of the heat capacity of the system with the maximum value obtained by treating the two horizons in the NLC-dS spacetime as a two-energy-level system of two distinct energies. This conclusion reflects the quantum properties of the coexistence region with two horizons in the NLC-dS spacetime. It provides a new avenue for further study of the thermodynamic properties of black holes and the quantum properties of de Sitter spacetime.
本文首先讨论了非线性带电dS(NLC-dS)时空中黑洞和宇宙学地平线共存的条件和存在区域,随后讨论了两地平线共存区域时空中满足边界条件的热力学量,并给出了两地平线共存区域NLC-dS时空中的有效热力学量。在此基础上,探讨了双水平面共存区域的热容量,发现上述区域中 NLC-dS 时空中的热容量表现出肖特基比热的特征。为了研究时空中热容量的内在原因,我们把 NLC-dS 时空中的两个水平面视为两个不同的能级,因此不同水平面的微观粒子表现出不同的能量。利用普通热力学系统中两能级之间的热容量关系来讨论 dS 时空中的热容量,可以发现热容量的行为与普通热力学系统中两能级的行为类似。通过比较系统热容量的最大值与把 NLC-dS 时空中的两个水平面视为具有两种不同能量的双能级系统所得到的最大值,可以近似地计算出双能级系统中的微观粒子数量。这一结论反映了 NLC-dS 时空中两个水平面共存区域的量子特性。它为进一步研究黑洞的热力学性质和德西特时空的量子性质提供了新的途径。
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引用次数: 0
Atomic electron transitions of hydrogen-like atoms induced by gravitational waves 引力波诱导的类氢原子的原子电子跃迁
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-22 DOI: 10.1088/1361-6382/ad861c
Bo-Hung Chen and Dah-Wei Chiou
As a realistic model of a quantum system of matter, this paper investigates the gravitational-wave effects on a hydrogen-like atom using a first-principles approach. By formulating the tetrad formalism of linearized gravity, we naturally incorporate gravitational-wave effects through minimal coupling in the covariant Dirac equation. The atomic electron transition rates induced by the gravitational wave are calculated using first-order perturbation theory, revealing a distinctive selection rule along with Fermi’s golden rule. This rule can be elegantly understood in terms of gravitons as massless spin-2 particles. Our results suggest the existence of gravitons and may lead to a novel approach to probing ultra-high-frequency gravitational waves.
作为量子物质系统的现实模型,本文采用第一原理方法研究了引力波对类氢原子的影响。通过提出线性化引力的四元形式主义,我们在协变狄拉克方程中通过最小耦合自然地纳入了引力波效应。引力波诱导的原子电子转换率是通过一阶扰动理论计算得出的,它揭示了费米黄金定律的独特选择规则。这一规则可以用引力子作为无质量自旋-2 粒子来优雅地理解。我们的研究结果表明引力子的存在,并可能为探测超高频引力波带来一种新方法。
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引用次数: 0
A review of gravitational memory and BMS frame fixing in numerical relativity 数值相对论中的引力记忆和 BMS 框架固定评述
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-21 DOI: 10.1088/1361-6382/ad83c2
Keefe Mitman, Michael Boyle, Leo C Stein, Nils Deppe, Lawrence E Kidder, Jordan Moxon, Harald P Pfeiffer, Mark A Scheel, Saul A Teukolsky, William Throwe and Nils L Vu
Gravitational memory effects and the BMS freedoms exhibited at future null infinity have recently been resolved and utilized in numerical relativity simulations. With this, gravitational wave models and our understanding of the fundamental nature of general relativity have been vastly improved. In this paper, we review the history and intuition behind memory effects and BMS symmetries, how they manifest in gravitational waves, and how controlling the infinite number of BMS freedoms of numerical relativity simulations can crucially improve the waveform models that are used by gravitational wave detectors. We reiterate the fact that, with memory effects and BMS symmetries, not only can these next-generation numerical waveforms be used to observe never-before-seen physics, but they can also be used to test GR and learn new astrophysical information about our Universe.
引力记忆效应和在未来空无穷大时表现出的 BMS 自由最近已在数值相对论模拟中得到解决和利用。由此,引力波模型和我们对广义相对论基本性质的理解得到了极大的改善。在本文中,我们回顾了记忆效应和 BMS 对称性背后的历史和直觉,它们在引力波中的表现形式,以及控制数值相对论模拟中无限多的 BMS 自由度如何能极大地改进引力波探测器所使用的波形模型。我们重申,有了记忆效应和 BMS 对称性,这些下一代数值波形不仅可以用来观测前所未见的物理现象,还可以用来检验引力波,了解我们宇宙的新天体物理信息。
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引用次数: 0
Towards quantum gravity with neural networks: solving the quantum Hamilton constraint of U(1) BF theory 用神经网络实现量子引力:求解 U(1) BF 理论的量子汉密尔顿约束
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-21 DOI: 10.1088/1361-6382/ad84af
Hanno Sahlmann and Waleed Sherif
In the canonical approach of loop quantum gravity, arguably the most important outstanding problem is finding and interpreting solutions to the Hamiltonian constraint. In this work, we demonstrate that methods of machine learning are in principle applicable to this problem. We consider U(1) BF theory in three dimensions, quantised with loop quantum gravity methods. In particular, we formulate a master constraint corresponding to Hamilton and Gauß constraints using loop quantum gravity methods. To make the problem amenable for numerical simulation we fix a graph and introduce a cutoff on the kinematical degrees of freedom, effectively considering BF theory at a root of unity. We show that the neural network quantum state ansatz can be used to numerically solve the constraints efficiently and accurately. We compute expectation values and fluctuations of certain observables and compare them with exact results or exact numerical methods where possible. We also study the dependence on the cutoff.
在环量子引力的经典方法中,可以说最重要的未决问题是寻找和解释哈密顿约束的解。在这项工作中,我们证明机器学习方法原则上适用于这一问题。我们考虑了三维空间的 U(1) BF 理论,并用环量子引力方法将其量子化。特别是,我们利用环量子引力方法制定了与汉密尔顿和高斯约束相对应的主约束。为了使问题适合于数值模拟,我们固定了一个图,并引入了运动自由度的截止,有效地考虑了统一根的 BF 理论。我们的研究表明,神经网络量子态解析法可以高效、准确地对约束条件进行数值求解。我们计算了某些观测值的期望值和波动,并尽可能与精确结果或精确数值方法进行比较。我们还研究了对截止的依赖性。
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引用次数: 0
Anomalous higher order Ward identities in tensorial group field theories without closure constraint 无闭合约束张元群场论中的反常高阶沃德特性
IF 3.5 3区 物理与天体物理 Q2 ASTRONOMY & ASTROPHYSICS Pub Date : 2024-10-21 DOI: 10.1088/1361-6382/ad7c13
Bio Wahabou Kpera, Vincent Lahoche, Dine Ousmane Samary and Seke Fawaaz Zime Yerima
The Ward–Takahashi identities are considered as the generalization of the Noether currents available to quantum field theory and include quantum fluctuation effects. Usually, they take the form of relations between correlation functions, which ultimately correspond to the relation between coupling constants of the theory. For this reason, they play a central role in the construction of renormalized theory, providing strong relations between counter-terms. Since last years, they have been intensively considered in the construction of approximate solutions for nonperturbative renormalization group of tensorial group field theories. The construction of these identities is based on the formal invariance of the partition function under a unitary transformation, and Ward’s identities result from a first-order expansion around the identity. Due to the group structure of the transformation under consideration, it is expected that a first-order expansion is indeed sufficient. We show in this article that this does not seem to be the case for a complex tensor theory model, with a kinetic term involving a Laplacian.
沃德-高桥特性被认为是诺特电流在量子场论中的一般化,包括量子波动效应。通常,它们采取相关函数之间关系的形式,最终对应于理论耦合常数之间的关系。正因为如此,它们在重规范化理论的构建中发挥着核心作用,提供了反作用项之间的强关系。近年来,在构建张量组场论的非微扰重正化群的近似解时,对它们进行了深入研究。这些等式的构建基于单元变换下分区函数的形式不变性,而沃德等式则来自于围绕等式的一阶展开。由于所考虑的变换具有群结构,因此预计一阶展开确实足够了。我们在这篇文章中证明,对于复杂张量理论模型来说,情况似乎并非如此。
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引用次数: 0
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Classical and Quantum Gravity
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