Spacetime might not be doomed after all

On the (non)genericity of the Kiselev spacetime

In many works in the literature, the Kiselev spacetime is interpreted as the "blackhole surrounded by quintessence"; an interpretation not really tenable. For example, it has recently been pointed out that the expressions "perfect fluid" and "quintessence" are used improperly in most of the articles that build on that spacetime; hence it is not as relevant as many of those authors might think. Here we point out that the original derivation of the Kiselev spacetime involves the use of too many coordinate conditions as well, again strongly restricting its relevance.

时空泡沫

Spacetime foam

时空是由气泡或环的波动排列组成的，称为时空泡沫或量子泡沫。我们用全息原理推导了它的结构，并证明了这一结果与涉及时空测量的格丹肯实验是一致的。我们建议使用基于激光的原子干涉技术来寻找时空波动。我们的分析清楚地表明，量子泡沫的物理学与黑洞的物理学密不可分。因此，一个负的实验结果可能会对半经典引力和黑洞物理学产生重要的影响。

Pathologies in Asymptotically Lifshitz Spacetimes

There has been significant interest in the last several years in studying possible gravitational duals, known as Lifshitz spacetimes, to anisotropically scaling field theories by adding matter to distort the asymptotics of an AdS spacetime. We point out that putative ground state for the most heavily studied example of such a spacetime, that with a flat spatial section, suffers from a naked singularity and further point out this singularity is not resolvable by any known stringy effect. We review the reasons one might worry that asymptotically Lifshitz spacetimes are unstable and employ the in…

Non-perturbative spectrum of non-local gravity

We investigate the non-perturbative degrees of freedom of a class of weakly non-local gravitational theories that have been proposed as an ultraviolet completion of general relativity. At the perturbative level, it is known that the degrees of freedom of non-local gravity are the same of the Einstein--Hilbert theory around any maximally symmetric spacetime. We prove that, at the non-perturbative level, the degrees of freedom are actually eight in four dimensions, contrary to what one might guess on the basis of the "infinite number of derivatives" present in the action. It is shown that six of…

奇异光滑性、非对易几何与粒子物理

Exotic smoothness, noncommutative geometry and particle physics

我们研究如何异国情调的微分结构可能会揭示自己在粒子物理学。分析是基于A.康纳斯对标准模型的构建。它表明，如果时空流形的副本之一是配备了一个奇异的微分结构，紧凑的对象的几何起源可能存在，即使时空是拓扑平凡的。可能的影响进行了讨论。构造了一个$SU(3)\otimes SU(2)\otimes U(1)$规范模型。这个模型可能并不现实，但它表明了由于时空流形上奇异微分结构的存在，可能会出现什么样的物理现象。

On the nonlinear instability of confined geometries

The discovery of a "weakly-turbulent" instability of anti-de Sitter spacetime supports the idea that confined fluctuations eventually collapse to black holes and suggests that similar phenomena might be possible in asymptotically-flat spacetime, for example in the context of spherically symmetric oscillations of stars or nonradial pulsations of ultracompact objects. Here we present a detailed study of the evolution of the Einstein-Klein-Gordon system in a cavity, with different types of deformations of the spectrum, including a mass term for the scalar and Neumann conditions at the boundary. W…

关于QGR弯曲时空极限的QFT第一章：总体方案

Towards the QFT on Curved Spacetime Limit of QGR. I: A General Scheme

在这篇文章和一个配套文件中，我们解决的问题，如何可能获得普通物质量子场（QFT）的弯曲时空（CST）从完整的量子广义相对论（QGR），从第一性原理开始传播的半经典极限。我们强调，我们并不声称对这个问题有一个满意的答案，而是我们的意图是通过展示在执行这样一个计划时必须解决的问题来引发讨论。在本文中，我们提出了一个计划，可以遵循，以达到这样的限制。我们将讨论在这样做时出现的技术和概念问题，以及如何在原则上解决这些问题。正如所料，由于QGR是一个背景独立的理论，全新的问题出现。例如，从根本上讲，光子的概念不仅涉及麦克斯韦量子场，而且涉及度规算符--在某种意义上，没有光子真空态，而是一个“光子真空算符”！虽然在第一篇论文中，我们专注于概念和抽象方面，例如（基本）n粒子状态（例如光子）的定义，但在第二篇论文中，我们进行了详细的计算，其中包括相干状态期望值和随机晶格上的传播。这些计算可以作为一个例子，说明用目前的数学技术可以达到什么程度。虽然它们导致了对第一量子修正（如伽马射线暴效应）大小的详细预测，但这些预测不应被太认真地对待，因为a）计算仅在运动学水平上进行; b）虽然我们可以对我们的结构中的自由度进行分类，但对可能选择的物理意义的分析才刚刚开始。

探究时空的时间可定向性

Probing time orientability of spacetime

本文提出利用量子真空电磁涨落影响带电粒子随机运动，构建统计时间可定向性指示量，以其反转模式局部识别 Minkowski 时空的时间不可定向拓扑。

Post-Newtonian particle physics in curved spacetime

In three very recent papers, (an initial paper by Morishima and Futamase, and two subsequent papers by Morishima, Futamase, and Shimizu), it has been argued that the observed experimental anomaly in the anomalous magnetic moment of the muon might be explained using general relativity. It is my melancholy duty to report that these articles are fundamentally flawed in that they fail to correctly implement the Einstein equivalence principle of general relativity. Insofar as one accepts the underlying logic behind these calculations (and so rejects general relativity) the claimed effect due to the…