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arXiv 1503.03030gr-qchep-th
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一阶2+1引力能

Energy in first order 2+1 gravity

Alejandro Corichi, Irais Rubalcava-Garcia

摘要:

本文考虑$Λ$ =0的三维重力场,边界条件渐近平坦. Ashtekar和Varadarajan在二阶形式主义中研究了这个系统-度量变量-他们表明Regge-Teitelboim形式主义产生了一致的哈密顿描述,令人惊讶的是,能量从下面和上面都有界。然而,时空的能量在任意常数下是确定的。自然的选择是修正这种自由,使闵可夫斯基时空的能量为零。最近,Marolf和Patiño从补充了Gibbons-Hawking项的Einstein-Hilbert作用量出发,表明在理论的2+1分解中,能量从Ashtekar-Varadarajan分析中转移,使得闵可夫斯基时空具有负能量。在这篇文章中,我们考虑的一阶形式主义,其中的基本变量是一个so(2,1)连接$ω_a{^I}_J$和一个三元组$e_a^I$。我们考虑两个行动。将四维Palatini引力的一致作用量自然地推广到三维,证明了它是有限的和可微的。对于这个作用,2+1分解(我们使用两种方法执行)产生对应于能量的哈密顿边界项。它赋予闵可夫斯基时空零能量。然后,我们提出了一个完全规范不变的作用量,并证明了它也是定义良好和可微的。有趣的是,它在壳层上与3D Palatini作用量通过一个加性常数相关,其相关能量由Marolf-Patiño表达式给出。因此,我们的结论是,从一阶形式主义的角度来看,闵可夫斯基时空可以始终具有零能量或等于-1/4G的负能量,这取决于作为起点的一致作用量的选择。

英文摘要:

We consider $Λ$=0 three dimensional gravity with asymptotically flat boundary conditions. This system was studied by Ashtekar and Varadarajan within the second order formalism -with metric variables- who showed that the Regge-Teitelboim formalism yields a consistent Hamiltonian description where, surprisingly, the energy is bounded from below and from above. The energy of the spacetime is, however, determined up to an arbitrary constant. The natural choice was to fix that freedom such that Minkowski spacetime has zero energy. More recently, Marolf and Patiño started from the Einstein-Hilbert action supplemented with the Gibbons-Hawking term and showed that, in the 2+1 decomposition of the theory, the energy is shifted from the Ashtekar-Varadarajan analysis in such a way that Minkowski spacetime possesses a negative energy. In this contribution we consider the first order formalism, where the fundamental variables are a so(2,1) connection $ω_a{^I}_J$ and a triad $e_a^I$. We consider two actions. A natural extension to 3 dimensions of the consistent action in 4D Palatini gravity is shown to be finite and differentiable. For this action, the 2+1 decomposition (that we perform using two methods) yields a Hamiltonian boundary term that corresponds to energy. It assigns zero energy to Minkowski spacetime. We then put forward a totally gauge invariant action, and show that it is also well defined and differentiable. Interestingly, it turns out to be related, on shell, to the 3D Palatini action by an additive constant in such a way that its associated energy is given by the Marolf-Patiño expression. Thus, we conclude that, from the perspective of the first order formalism, Minkowski spacetime can consistently have either, zero, or a negative energy equal to -1/4G, depending on the choice of consistent action employed as starting point.

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