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arXiv · 2510.18750

Backreactions from loading the stable photon sphere in Weyl conformal gravity

Reinosuke Kusano·Keith Horne·Friedrich Koenig·Miguel Yulo Asuncion
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Abstract

We investigate the accumulation of null matter at the stable photon sphere in the Mannheim-Kazanas metric, the analogue to the Schwarzschild solution in Weyl's conformal theory of gravity. In our toy problem in which we consider an infinitely-thin shell, we find that a jump in radial pressure ${T^r}_r$ is induced across the shell unless the shell has a radius of either the unstable or stable photon sphere radii. We then find that upon loading the stable photon sphere, its area remains invariant. Furthermore, at a critical threshold loading limit for this zero-width null matter shell, we are able to produce a metric containing an extremal horizon with an AdS$_2\times$S$^2$ geometry completely independent of the cosmological curvature. This hitherto unencountered and therefore unexpected result is a phenomenon unseen in standard nonconformal second-order metrics with nonzero cosmological constants.

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Reinosuke Kusano, Keith Horne, Friedrich Koenig, Miguel Yulo Asuncion. 2025-10-21. Backreactions from loading the stable photon sphere in Weyl conformal gravity. https://doi.org/10.1088/1361-6382%2Fae415f

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