In this note, we characterize 1 + n doubly twisted spacetimes in terms of “doubly torqued” vector fields. They extend Bang–Yen Chen’s characterization of twisted and generalized Robertson–Walker spacetimes with torqued and concircular vector fields. The result is a simple classification of 1 + n doubly-twisted, doubly-warped, twisted and generalized Robertson–Walker spacetimes.

中文翻译：

---

双重扭曲时空的简单表征

在本说明中，我们描述了1 + n就“双扭曲”矢量场而言，双重扭曲的时空。他们扩展了 Bang-Yen Chen 对扭曲和广义 Robertson-Walker 时空的描述，其中包含扭转和同圆矢量场。结果是一个简单的分类1 + n双重扭曲、双重扭曲、扭曲和广义的罗伯逊-沃克时空。