https://doi.org/10.1140/epjc/s10052-026-16006-2
Regular Article - Theoretical Physics
Black hole shadows in nonminimally coupled Weyl connection gravity
1
OKEANOS–Instituto de Investigação em Ciências do Mar, Universidade dos Açores, Rua Prof. Doutor Frederico Machado, 4, 9900-140, Horta, Portugal
2
Centro de Física das Universidades do Minho e do Porto, Rua do Campo Alegre s/n, 4169-007, Porto, Portugal
3
Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001, Lisboa, Portugal
4
Centro de Análise Matemática, Geometria e Sistemas Dinâmicos, Departamento de Matemática, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001, Lisbon, Portugal
5
Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016, Lisbon, Portugal
6
Departamento de Física, Faculdade de Ciências da Universidade de Lisboa, Edifício C8, Campo Grande, 1749-016, Lisbon, Portugal
a
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Received:
26
March
2026
Accepted:
14
June
2026
Published online:
26
June
2026
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–Nordström-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 
and requiring consistency at the 
level, we obtain 
(model I), 
(model II), and 
(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.
© The Author(s) 2026
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Funded by SCOAP3.
