1、Aging and Holography

这篇文章的题目就很吸引人，衰老可以用全息理论来描述！

这篇文章的引言说得很吸引人：如果将一个平衡态系统通过突然的变化变成非平衡的，那么这个系统会进入缓慢的演化状态，时间平移不变性消失了，而且会出现动力学标度律。

但用来描述衰老的数学结构是否过于简单了？他们提出的衰老对称群是这么获得的：从一个具备Lifshitz对称性的时空出发，获得一个对称群，生成元是时间平移，空间平移，伽利略boosts，空间转动，dilatation，特殊共形变换。然后扔掉时间平移，这个新的对称代数叫做衰老代数。有这样对称性的时空可以是依赖时间的时空。

虽然值得怀疑，我觉得文章应该得到应有的注意。作者之一是Djordje Minic。

摘要：

Aging phenomena are examples of `non-equilibrium criticality’ and can be exemplified by systems with Galilean and scaling symmetries but no time translation invariance. We realize aging holographically using a deformation of a non-relativistic version of gauge/gravity duality. Correlation functions of scalar operators are computed using holographic real-time techniques, and agree with field theory expectations. At least in this setup, general aging phenomena are reproduced holographically by complexifying the bulk space-time geometry, even in Lorentzian signature.

因为这篇文章与我和庞毅的工作有关，当然得转。

这篇文章复述作者们以前的一个工作，献给A. A. Slavnov七十寿辰的。他们证明，如果我们想改变Einstein理论，仅保留空间重新参数化不变性，得到的理论通常是不自洽的，因为Hamiltonian约束是第二类的，要求lapse函数N=0，当然非物理。

摘要：

Gauge symmetries lead to first-class constraints. This assertion is of course true only for non trivial gauge symmetries, i.e., gauge symmetries that act non trivially on-shell on the dynamical variables. We illustrate this well-appreciated fact for time reparametrization invariance in the context of modifications of gravity -suggested in a recent proposal by Horava-in which the Hamiltonian constraint is deformed by arbitrary spatial diffeomorphism invariant terms, where some subtleties are found to arise.

这篇文章和作者以前的文章一样，号称找到了Horava理论的自洽形式，但同时承认有第二类约束，我很奇怪他如何避免一般性的结论。他还说可以通过Batalin-Tyutin量子化方式获得只有第一类约束的形式。

反正我个人对Horava理论失去兴趣，不去认真研究这篇文章了。

摘要：

In this paper we continue the study of the Hamiltonian formalism of the healthy extended Horava-Lifshitz gravity. We find the constraint structure of given theory and argue that this is the theory with the second class constraints. Then we discuss physical consequence of this result. We also apply the Batalin-Tyutin formalism of the conversion of the system with the second class constraints to the system with the first class constraints to the case of the healthy extended Horava-Lifshitz theory. As a result we find new theory of gravity with structure that is different from the standard formulation of Horava-Lifshitz gravity or General Relativity.

这篇文章讨论凝聚态实现各种引力视界的可能，主要用的模型还是流体。

个人认为，超颖材料还是更有前途

摘要：

The concept of a horizon known from general relativity describes the loss of causal connection and can be applied to non-gravitational scenarios such as out-of-equilibrium condensed-matter systems in the laboratory. This analogy facilitates the identification and theoretical study (e.g., regarding the trans-Planckian problem) and possibly the experimental verification of “exotic” effects known from gravity and cosmology, such as Hawking radiation. Furthermore, it yields a unified description and better understanding of non-equilibrium phenomena in condensed matter systems and their universal features. By means of several examples including general fluid flows, expanding Bose-Einstein condensates, and dynamical quantum phase transitions, the concepts of event, particle, and apparent horizons will be discussed together with the resulting quantum effects.