1、New variables for the Einstein theory of gravitation
俄国著名数学物理学家L. D. Faddeev曾经利用分解提出所谓的规范场的Faddeev变量。现在,他将这个工作推广到度规。
他的想法很简单,任何四维流形(Euclidean or Lorentzian Riemannian)都由有10个分量的度规描述,所以可以嵌入10维欧几里德空间。这样,度规可以被10个嵌入函数取代。Faddeev建议,干脆用10个矢量场,当然这样就有40个分量,太多了。他建议引入约束
但对运动方程的分析发现这些约束并不是必须的。要知道具体细节,建议看Faddeev的文章。
Ashtekar引入所谓Ashtekar变量导致loop quantum gravity,不知道Faddeev变量是否会导致一个新的理论。
最近看很多人看过的BBT,其中天才Sheldon是研究弦论的,而另一个天才Leslie是loop quantum gravity的拥趸。后来出现了一个北韩来的天才Kim,才14岁,已经看到了弦论有很多亚稳态真空,让Sheldon感到很失落。Kim是唯一可以和Sheldon以及Leslie抗衡的天才,不知道他对Faddeev的工作怎么看?
2、Holographic calculation of hadronic contributions to muon g-2
基于全息原理的AdS/CFT很有用。在强相互作用方面,已经发展到可以计算某些散射振幅甚至强子对muon的反常磁矩的贡献了。
啥也不说,直接拷贝该文的摘要:
Using the gauge/gravity duality, we compute the leading order hadronic (HLO) contribution to the anomalous magnetic moment of muon, amu(HLO). Holographic renormalization is used to obtain a finite vacuum polarization. We find in AdS/QCD with two light flavors, which is compared with the currently revised BABAR data estimated from e^+ e^- -> pi^+ pi^- events, .3、Can the Arrow of Time be understood from Quantum Cosmology?
粗略地看了一下这篇文章,似乎建议在Wheeler-deWitt方程中,宇宙半径就是时间箭头,因为该方程对于宇宙大小来说的确是不对称的。这么一个简单的道理是否能解释时间的箭头(即宇宙为什么开始于低熵状态)?也许不能。作者没有给出太多的论证。但有时最简单的理由没准就是正确的理由。
摘要:
I address the question whether the origin of the observed arrow of time can be derived from quantum cosmology. After a general discussion of entropy in cosmology and some numerical estimates, I give a brief introduction into quantum geometrodynamics and argue that this may provide a sufficient framework for studying this question. I then show that a natural boundary condition of low initial entropy can be imposed on the universal wave function. The arrow of time is then correlated with the size of the Universe and emerges from an increasing amount of decoherence due to entanglement with unobserved degrees of freedom. Remarks are also made concerning the arrow of time in multiverse pictures and scenarios motivated by dark energy.
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