标题： 在零动量费米坐标中扩展双复制 显示英文标题

标题： Expanding on the double copy in null Fermi coordinates

摘要： 我们提出了一种围绕类光测地线的费米规范坐标展开的Weyl经典双照方法。在这一“Penrose展开”的主导阶，我们恢复了之前提出的Penrose极限的双照方法。对于具有精确双照结构的时空，这种Penrose极限双照方法可以扩展到所有阶。对于没有此类双照结构的时空，在第二亚主导阶会出现一般的障碍。因此，我们认为对于任何时空，在任何类光测地线附近，至少在Penrose展开的第一亚主导阶内，存在经典的双照结构。最后，我们指出在识别一个适当的平直空间以将我们的结果扩展到Kerr-Schild双照方法时存在困难，这与Kerr-Schild和Penrose-Güven规范之间的普遍不相容性有关。 显示英文摘要

摘要： We propose a Weyl classical double copy for a Fermi normal coordinate expansion around null geodesics. To leading order in this "Penrose expansion", we recover a previously proposed double copy of the Penrose limit. For spacetimes with an exact double copy, this Penrose limit double copy is extended to all orders. For spacetimes without such a double copy, generic obstructions appear at second subleading order. We thus argue that for any spacetime, near any null geodesic there is a classical double copy structure at least up to first subleading order in the Penrose expansion. Finally, we point out a difficulty in identifying an appropriate flat space to extend our results to the Kerr-Schild double copy, related to the generic incompatibility between Kerr-Schild and Penrose-G\"uven gauge.