V1: 18 pages; V2: reformatted, now 14 pages; some clarifications added; no significant physics changes. This version accepted for publication in Classical and Quantum Gravity
The Hawking-Ellis (Segre-Plebanski) classification of possible stress-energy tensors is an essential tool in analyzing the implications of the Einstein field equations in a more-or-less model-independent manner. In the current article the basic idea is to simplify the Hawking-Ellis type I, II, III, and IV classification by isolating the "essential core" of the type II, type III, and type IV stress-energy tensors; this being done by subtracting (special cases of) type I to simplify the (Lorentz invariant) eigenvalue structure as much as possible without disturbing the eigenvector structure. We will denote these "simplified cores" type II$_0$, type III$_0$, and type IV$_0$. These "simplified cores" have very nice and simple algebraic properties. Furthermore, types I and II$_0$ have very simple classical interpretations, while type IV$_0$ is known to arise semi-classically (in renormalized expectation values of standard stress-energy tensors). In contrast type III$_0$ stands out in that it has neither a simple classical interpretation, nor even a simple semi-classical interpretation. We will also consider the robustness of this classification considering the stability of the different Hawking-Ellis types under perturbations. We argue that types II and III are definitively unstable, whereas types I and IV are stable.
Disformal Maps: Classification and Singular Dynamics
Institute for Basic Science (IBS)（基础科学研究所）；CEICO - Central European Institute for Cosmology and Fundamental Physics, FZU - Institute of Physics of the Czech Academy of Sciences（中欧宇宙学与基础物理中心、捷克科学院物理研究所）；Department of Physics, Institute of Science Tokyo（东京科学大学物理系）；Department of Physics & Institute of Physics and Applied Physics (IPAP), Yonsei University（延世大学物理系与应用物理研究所）
Noise Kernel and Stress Energy Bi-Tensor of Quantum Fields in Hot Flat Space and Gaussian Approximation in the Optical Schwarzschild Metric
继续研究弯曲时空中噪声核的正则化[N。G. Phillips和B. L. Hu，Phys. Rev. D { \bf 63}，104001（2001）]中，我们对光学时空类采用了改进的点分离方案，采用了Bekenstein-Parker-Page的格林函数的高斯近似。在第一个例子中，我们推导出正则化的噪声核的热场在平坦空间。这对于黑洞成核的考虑是有用的。在光学史瓦西时空的第二个例子中，我们得到了视界处噪声核的有限表达式，并恢复了无穷远处热平坦空间的结果。噪声核的知识对于研究黑洞视界涨落和霍金辐射反反应等问题是必不可少的。我们表明，高斯近似格林函数的工作令人惊讶的是，在史瓦西视界的应力张量产生显着的误差，在噪声内核。我们确定故障发生在第四协变导数阶。
