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arXiv 1203.2158hep-th
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“四元唯一”理论空间:非微扰重整化流和渐近安全性

The "tetrad only" theory space: Nonperturbative renormalization flow and Asymptotic Safety

Ulrich Harst, Martin Reuter

摘要:

在迄今为止尚未探索的“仅四分体”理论空间上,建立了非微扰引力粗粒化流和相应的泛函重整化群方程。它包括依赖于四元组场(以及相关的背景场和鬼场)的作用泛函,并且在时空同态和局部洛伦兹变换的半直积下是不变的。这个理论空间与量子爱因斯坦引力(QEG)的不同之处在于,四元组而不是度规构成了基本变量,并且因为局部洛伦兹不变性的额外对称性要求。由于自旋联系不再是独立的场变量,它也不同于最近研究的量子爱因斯坦-嘉当引力。我们显式计算的重整化群流的Einstein-Hilbert截断的四分之一版本内的这个理论空间。为了评估基本场变量的选择对引力平均作用的重整化行为的影响,与QEG和QECG中的模拟结果进行了详细的比较,并研究了渐近安全无限截止极限的可能性。本文还讨论了耦合到量子引力的费米子物质的非微扰研究的意义。事实证明,在泛函流方程的上下文中,文献中提出的“混合计算”(仅在费米子图中使用四元组,在所有其他图中使用度规)不太可能是定量可靠的。此外,我们发现,与微扰理论,非传播的Faddeev-Popov鬼有关的本地洛伦兹变换可能不会被丢弃,而是相当显着的贡献的β函数的牛顿常数和宇宙学常数。

英文摘要:

We set up a nonperturbative gravitational coarse graining flow and the corresponding functional renormalization group equation on the as to yet unexplored "tetrad only" theory space. It comprises action functionals which depend on the tetrad field (along with the related background and ghost fields) and are invariant under the semi-direct product of spacetime diffeomorphisms and local Lorentz transformations. This theory space differs from that of Quantum Einstein Gravity (QEG) in that the tetrad rather than the metric constitutes the fundamental variable and because of the additional symmetry requirement of local Lorentz invariance. It also differs from "Quantum Einstein Cartan Gravity" (QECG) investigated recently since the spin connection is not an independent field variable now. We explicitly compute the renormalization group flow on this theory space within the tetrad version of the Einstein-Hilbert truncation. A detailed comparison with analog results in QEG and QECG is performed in order to assess the impact the choice of a fundamental field variable has on the renormalization behavior of the gravitational average action, and the possibility of an asymptotically safe infinite cutoff limit is investigated. Implications for nonperturbative studies of fermionic matter coupled to quantum gravity are also discussed. It turns out that, in the context of functional flow equations, the "hybrid calculations" proposed in the literature (using the tetrad for fermionic diagrams only, and the metric in all others) are unlikely to be quantitatively reliable. Moreover we find that, unlike in perturbation theory, the non-propagating Faddeev-Popov ghosts related to the local Lorentz transformations may not be discarded but rather contribute quite significantly to the beta functions of Newton's constant and the cosmological constant.

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