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 beyond the Penrose limit. 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. Lastly, 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–Güven gauge.
Chawla, Samarth, et al. "Expanding on the double copy in null Fermi coordinates." Classical and Quantum Gravity, vol. 42, no. 17, Aug. 2025. https://doi.org/10.1088/1361-6382/adf6fc
Chawla, Samarth, Fransen, Kwinten, and Keeler, Cynthia, "Expanding on the double copy in null Fermi coordinates," Classical and Quantum Gravity 42, no. 17 (2025), https://doi.org/10.1088/1361-6382/adf6fc
@article{osti_2585164,
author = {Chawla, Samarth and Fransen, Kwinten and Keeler, Cynthia},
title = {Expanding on the double copy in null Fermi coordinates},
annote = {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 beyond the Penrose limit. 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. Lastly, 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–Güven gauge.},
doi = {10.1088/1361-6382/adf6fc},
url = {https://www.osti.gov/biblio/2585164},
journal = {Classical and Quantum Gravity},
issn = {ISSN 0264-9381},
number = {17},
volume = {42},
place = {United States},
publisher = {IOP Publishing},
year = {2025},
month = {08}}
Proceedings of Corfu Summer Institute 2017 "Schools and Workshops on Elementary Particle Physics and Gravity" — PoS(CORFU2017)https://doi.org/10.22323/1.318.0177