We present an overview of both older and recent developments concerning scale separation in string theory. We focus on parametric scale separation obtained at the classical level in flux compactifications down to AdS vacua. We review the scenarios that have been proposed to achieve a hierarchy of scales between spacetime and the internal space, built from a low-dimensional perspective. We then discuss how they have been understood to arise from proper higher-dimensional descriptions. Eventually, limitations of these constructions as well as Swampland and holographic arguments addressing the question of scale separation in string theory are discussed. The purpose of the review is to draw an accurate picture of the state of the art of the subject at the moment.

中文翻译：

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隐藏额外维度：弦理论中尺度分离的回顾

我们概述了弦理论中尺度分离的较早和最近的发展。我们专注于在通量紧致化至 AdS 真空的经典水平上获得的参数尺度分离。我们回顾了为实现时空和内部空间之间的尺度层次结构而提出的方案，这些方案是从低维角度构建的。然后我们讨论如何理解它们是从适当的高维描述中产生的。最后，讨论了这些结构的局限性以及解决弦理论中尺度分离问题的沼泽和全息论证。审查的目的是准确描绘当前主题的最新技术状况。