The simple structure of doubly torqued vectors allows for a natural characterization of doubly twisted down to warped spacetimes, as well as Kundt spacetimes down to PP waves. For the first ones the vectors are timelike, for the others they are null. We also discuss some properties, and their connection to hypersurface orthogonal conformal Killing vectors, and null Killing vectors.

中文翻译：

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双扭转矢量和双扭曲和Kundt时空的分类

双扭曲矢量的简单结构允许对扭曲到时空的双向扭曲以及从PP波到Kundt时空的自然表征。对于第一个，向量是类似时间的，对于其他向量，它们是空的。我们还将讨论一些属性，以及它们与超表面正交共形Killing向量和null Killing向量的关系。