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arXiv 1702.03577hep-thgr-qc
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物理重整化方案与量子引力的渐近安全性

Physical renormalization schemes and asymptotic safety in quantum gravity

Kevin Falls

摘要:

将重整化群方法和$\varepsilon$展开方法应用于量子引力,揭示了在大于2维的时空中存在渐近安全的不动点。为了促进这一点,利用物理重整化方案,其中重整化群流方程采取与物理自由度的参数化无关的形式(即,规范固定条件和场变量的选择)。相反,流量方程取决于参考观测量的反常维数。在存在时空边界的情况下,我们发现β函数保持了爱因斯坦-希尔伯特作用量和吉布斯-霍金-约克边界项之间的平衡。利用二维附近的$\varepsilon$展开,我们考虑了爱因斯坦引力与物质的耦合。由于二维Weyl不变性的破坏,方案独立性通常被循环扩展所掩盖。在保持二维Weyl不变性的方案中,我们避免了循环展开,并找到了唯一的紫外(UV)不动点。在这个固定点上,反常维数很大,必须对所有的循环阶数求和才能得到临界指数。通过重新计算,我们发现了一组普遍的标度维数,这些标度维数表明只有有限数量的物质相互作用是相关的。这是量子引力是可重整化的一个强有力的迹象。

英文摘要:

The methods of the renormalization group and the $\varepsilon$-expansion are applied to quantum gravity revealing the existence of an asymptotically safe fixed point in spacetime dimensions higher than two. To facilitate this, physical renormalization schemes are exploited where the renormalization group flow equations take a form which is independent of the parameterisation of the physical degrees of freedom (i.e. the gauge fixing condition and the choice of field variables). Instead the flow equation depends on the anomalous dimensions of reference observables. In the presence of spacetime boundaries we find that the required balance between the Einstein-Hilbert action and Gibbons-Hawking-York boundary term is preserved by the beta functions. Exploiting the $\varepsilon$-expansion near two dimensions we consider Einstein gravity coupled to matter. Scheme independence is generically obscured by the loop-expansion due to breaking of two-dimensional Weyl invariance. In schemes which preserve two-dimensional Weyl invariance we avoid the loop expansion and find a unique ultra-violet (UV) fixed point. At this fixed point the anomalous dimensions are large and one must resum all loop orders to obtain the critical exponents. Performing the resummation a set of universal scaling dimensions are found. These scaling dimensions show that only a finite number of matter interactions are relevant. This is a strong indication that quantum gravity is renormalizable.

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