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arXiv · 2603.08441

Black hole shadows in nonminimally coupled Weyl connection gravity

Cláudio Gomes·Margarida Lima·Francisco S. N. Lobo·Luís F. Dias da Silva
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Abstract

We study black hole shadows in nonminimally coupled Weyl connection gravity, a metric-affine extension of general relativity in which spacetime is described by a metric and a Weyl vector field encoding non-metricity. Despite going beyond the Riemannian framework, the presence of a non-dynamical Weyl vector ensures second-order field equations. The theory admits Schwarzschild- and Reissner--Nordstr\"{o}m-like solutions modified by a Weyl integration constant that parametrizes deviations from General Relativity. By computing the corresponding shadow radii and confronting them with the Event Horizon Telescope constraints on Sgr A*, we place observational bounds on the Weyl parameter. Assuming an observer distance $r_O = 4.1\times 10^{10}M$ and requiring consistency at the $2\sigma$ level, we obtain $\omega \gtrsim 10^{11.7}M$ (model I), $\omega \gtrsim 10^{10.5}M$ (model II), and $\omega \sim 10^{12}M$ (model III). Our results show that present horizon-scale imaging already sets meaningful limits on spacetime non-metricity. This work highlights the power of black hole shadow observations as probes of extended gravitational dynamics and establishes a direct link between Weyl-based theories and current astrophysical data.

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Cláudio Gomes, Margarida Lima, Francisco S. N. Lobo, Luís F. Dias da Silva. 2026-03-09. Black hole shadows in nonminimally coupled Weyl connection gravity. https://doi.org/10.1140/epjc%2Fs10052-026-16006-2

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