Non-minimal light-curvature couplings and black-hole imaging
Abstract
Non-minimal couplings between the electromagnetic field strength and the spacetime curvature are part of the effective field theory of gravity and matter. They alter the local propagation of light in a significant way if the ratio of spacetime curvature to the non-minimal coupling is of order one. Spacetime curvature can become appreciable around black holes, and yet the effect of non-minimal couplings on electromagnetic observations of black holes remains underexplored. A particular feature of the non-minimal coupling between the electromagnetic field-strength and the Riemann tensor is that it generates two distinct photon rings for different polarizations. Working within the paradigm of lensing bands and focusing on the lensing band, we illustrate by which diagnostics a modified light propagation may be distinguished from a modified spacetime geometry and how constraints on the value of the non-minimal coupling can be obtained
Cite
@article{arxiv.2505.21431,
title = {Non-minimal light-curvature couplings and black-hole imaging},
author = {Raúl Carballo-Rubio and Héloïse Delaporte and Astrid Eichhorn and Pedro G. S. Fernandes},
journal= {arXiv preprint arXiv:2505.21431},
year = {2025}
}
Comments
16 pages; 7 figures; accepted for publication in PRD