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arXiv 1205.3583hep-thgr-qc
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运行边界作用、渐近安全和黑洞热力学

Running boundary actions, Asymptotic Safety, and black hole thermodynamics

D. Becker, M. Reuter

摘要:

以往的量子爱因斯坦引力(QEG)中的渐近安全性研究都是在没有边界的时空流形上,通过有效平均作用量及其相应的泛函重整化群(RG)方程进行的。在这里,我们采取了第一步的推广非平凡的边界,限制自己的行动泛函是最多的二阶导数作用于度量。我们分析了两个例子截断行动与运行的边界条件:完整的QEG内的单度量爱因斯坦-希尔伯特(EH)截断,增加了一个尺度相关的Gibbons-Hawking(GH)表面项,和一个双度量截断重力耦合到标量物质场。后者包含17个运行耦合,涉及到体积和边界项,其β函数计算在诱导重力近似。我们发现,体积和边界牛顿常数,属于EH和GH项,分别显示相反的RG运行;提出一个规模依赖的ADM质量的变体,我们认为,这两个耦合的运行是一致的重力反屏蔽。我们描述了一个简单的装置,用于计算红外截止尺度和紫外之间的场模式的数量。该方法表明,在渐近安全理论中,当RG轨迹保持在基本不动点的标度区域中时,有效地没有积分出的场模式。作为一个应用程序,我们调查的半经典理论的黑洞热力学得到修改的量子引力的影响,并比较新的图片旧的工作“RG改进的黑洞”,其中包括运行的体积牛顿常数。例如,我们发现,在普朗克尺度下,黑洞的熵消失了,比热容变为正值。

英文摘要:

Previous explorations of the Asymptotic Safety scenario in Quantum Einstein Gravity (QEG) by means of the effective average action and its associated functional renormalization group (RG) equation assumed spacetime manifolds which have no boundaries. Here we take a first step towards a generalization for non-trivial boundaries, restricting ourselves to action functionals which are at most of second order in the derivatives acting on the metric. We analyze two examples of truncated actions with running boundary terms: full fledged QEG within the single-metric Einstein-Hilbert (EH) truncation, augmented by a scale dependent Gibbons-Hawking (GH) surface term, and a bi-metric truncation for gravity coupled to scalar matter fields. The latter contains 17 running couplings, related to both bulk and boundary terms, whose beta-functions are computed in the induced gravity approximation. We find that the bulk and the boundary Newton constant, pertaining to the EH and GH term, respectively, show opposite RG running; proposing a scale dependent variant of the ADM mass we argue that the running of both couplings is consistent with gravitational anti-screening. We describe a simple device for counting the number of field modes integrated out between the infrared cutoff scale and the ultraviolet. This method makes it manifest that, in an asymptotically safe theory, there are effectively no field modes integrated out while the RG trajectory stays in the scaling regime of the underlying fixed point. As an application, we investigate how the semiclassical theory of Black Hole Thermodynamics gets modified by quantum gravity effects and compare the new picture to older work on `RG-improved black holes' which incorporated the running of the bulk Newton constant only. We find, for instance, that the black hole's entropy vanishes and its specific heat capacity turns positive at Planckian scales.

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