A class of curved spacetimes with global parabolic isometries (GPI) is introduced. These isometries have fixed point sets on two-dimensional null surfaces which can be interpreted as worldsheets of massless cosmic strings. Back reaction effects of the strings in such spacetimes can be described exactly, in terms of a nontrivial holonomy at the worldsheet. We show that the GPI spacetimes are type \(N\) geometries of the Petrov classification. We describe a number of features of these spacetimes, including properties of Killing horizons associated to GPI. As an example, we consider a circular massless cosmic string in the de Sitter universe and present the metric in new coordinates centered at the string worldsheet.

中文翻译：

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具有时空抛物异构体的时空无质量宇宙弦

引入了一类具有整体抛物线形等价线（GPI）的弯曲时空。这些等距在二维空表面上具有不动点集，这些空点可以解释为无质量宇宙弦的世界表。在这种时空下，弦的反作用效应可以根据世界上不平凡的整体性准确描述。我们证明GPI时空是Petrov分类的\（N \）型几何。我们描述了这些时空的许多特征，包括与GPI相关的Killing层级的属性。例如，我们考虑de Sitter宇宙中的圆形无质量宇宙线，并在以字符串世界表为中心的新坐标中显示度量。