We discuss three different (conformally) Carrollian geometries and their relation to null infinity from the unifying perspective of Cartan geometry. Null infinity per se comes with numerous redundancies in its intrinsic geometry and the two other Carrollian geometries can be recovered by making successive choices of gauge. This clarifies the extent to which one can think of null infinity as being a (strongly) Carrollian geometry and we investigate the implications for the corresponding Cartan geometries. The perspective taken, which is that characteristic data for gravity at null infinity are equivalent to a Cartan geometry for the Poincaré group, gives a precise geometrical content to the fundamental fact that ‘gravitational radiation is the obstruction to having the Poincaré group as asymptotic symmetries’.

中文翻译：

---

Carrollian 流形和零无穷大：Cartan 几何学的观点

我们从嘉当几何的统一角度讨论三种不同的（共形的）卡罗尔几何及其与零无穷大的关系。零无穷大本身其内在几何中存在大量冗余，并且可以通过连续选择规范来恢复其他两个 Carrollian 几何。这阐明了人们可以将零无穷大视为（强）卡罗尔几何的程度，并且我们研究了相应的嘉当几何的含义。所采用的观点是，零无穷处的引力特征数据等同于庞加莱群的嘉当几何，为“引力辐射阻碍庞加莱群渐近对称”这一基本事实提供了精确的几何内容.