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arXiv 1107.5041hep-thgr-qcmath-phmath.MP
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多分数维时空中的几何与场论

Geometry and field theory in multi-fractional spacetime

Gianluca Calcagni

摘要:

我们构建了一个理论的领域生活在连续几何与分数Hausdorff和光谱尺寸,专注于一个平坦的背景类似闵可夫斯基时空。在回顾了具有固定维数的分数空间的性质之后,在一篇配套论文中,我们推广到了受多重分形几何启发的多重分数场景,其中维数随尺度而变化。这与分数场论的重整化群性质有关,可以用标量场的例子来说明。根据拉格朗日量的对称性,可以定义两个模型。在其中一个中,有效维度在紫外线(UV)中从2开始流动,并且几何结构将红外线限制为四维。在UV临界值处,模型呈现为功率计数可重正化。然而,这并不是最根本的制度。分形几何的令人信服的论点需要扩展的分数行动措施复杂的秩序。在这样做时,我们得到一个层次的尺度特征不同的几何制度。在非常小的尺度上,离散对称性出现,连续时空的概念开始模糊,直到达到基本尺度和超微观分形结构。这种精细的几何层次结构对非对易理论和离散量子引力有着重要的意义。在后一种情况下,本模型可以被视为量子离散到经典连续过渡的自上而下的实现。

英文摘要:

We construct a theory of fields living on continuous geometries with fractional Hausdorff and spectral dimensions, focussing on a flat background analogous to Minkowski spacetime. After reviewing the properties of fractional spaces with fixed dimension, presented in a companion paper, we generalize to a multi-fractional scenario inspired by multi-fractal geometry, where the dimension changes with the scale. This is related to the renormalization group properties of fractional field theories, illustrated by the example of a scalar field. Depending on the symmetries of the Lagrangian, one can define two models. In one of them, the effective dimension flows from 2 in the ultraviolet (UV) and geometry constrains the infrared limit to be four-dimensional. At the UV critical value, the model is rendered power-counting renormalizable. However, this is not the most fundamental regime. Compelling arguments of fractal geometry require an extension of the fractional action measure to complex order. In doing so, we obtain a hierarchy of scales characterizing different geometric regimes. At very small scales, discrete symmetries emerge and the notion of a continuous spacetime begins to blur, until one reaches a fundamental scale and an ultra-microscopic fractal structure. This fine hierarchy of geometries has implications for non-commutative theories and discrete quantum gravity. In the latter case, the present model can be viewed as a top-down realization of a quantum-discrete to classical-continuum transition.

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