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arXiv 0905.3492gr-qc
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半经典量子引力:从图获得流形

Semiclassical Quantum Gravity: Obtaining Manifolds from Graphs

Luca Bombelli, Alejandro Corichi, Oliver Winkler

摘要:

我们解决离散几何的“逆问题”,它包括在确定是否,给定一个离散结构的类型,一般不意味着几何信息,甚至拓扑结构,可以与它相关联的一个独特的流形在适当的意义上,并构建流形时,它存在。这个问题出现在各种各样的方法来量子引力,假设一个离散的结构在基本水平上,目前的工作是由半经典部门的环路量子引力,所以我们将离散结构是一个图形和流形是时空中的空间切片。我们确定了一类图,那些其顶点有一个固定的价,这样的建设可以指定。我们定义了一个程序,旨在产生一个细胞复杂的图形,并表明,对于图形,它可以进行到完成,所产生的细胞复杂的事实上是一个PL-流形。我们的类的程序不能完成的图形不会出现作为边图的流形细胞分解,或可以被视为细胞分解的流形结构在小尺度(在细胞间距方面)。我们还简要地评论如何可以扩展我们的程序更一般的图形。

英文摘要:

We address the "inverse problem" for discrete geometry, which consists in determining whether, given a discrete structure of a type that does not in general imply geometrical information or even a topology, one can associate with it a unique manifold in an appropriate sense, and constructing the manifold when it exists. This problem arises in a variety of approaches to quantum gravity that assume a discrete structure at the fundamental level; the present work is motivated by the semiclassical sector of loop quantum gravity, so we will take the discrete structure to be a graph and the manifold to be a spatial slice in spacetime. We identify a class of graphs, those whose vertices have a fixed valence, for which such a construction can be specified. We define a procedure designed to produce a cell complex from a graph and show that, for graphs with which it can be carried out to completion, the resulting cell complex is in fact a PL-manifold. Graphs of our class for which the procedure cannot be completed either do not arise as edge graphs of manifold cell decompositions, or can be seen as cell decompositions of manifolds with structure at small scales (in terms of the cell spacing). We also comment briefly on how one can extend our procedure to more general graphs.

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