Hunting for extra dimensions in black hole shadows

Observational data of the Sagittarius A* (Sgr A*) shadow released by the Event Horizon Telescope are used to investigate eventual deviations in the black hole shadow radius, aiming to seek physics beyond the Standard Model coming from extra-dimensional theory. We consider the braneworld scenario described by the Randall-Sundrum model and determine the black hole shadow radius correction owing to the higher dimension. From data of the shadow radius in units of black hole mass determined by Keck- and Very Large Telescope Interferometer (VLTI)-based estimates, we imposed restrictions on the deviation obtained, and one sets an upper limit to the curvature radius of anti--de Sitter (${\mathrm{AdS}}_{5}$) spacetime ${\ensuremath{\ell}}_{(\text{Keck})}\ensuremath{\lesssim}3.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{AU}$ and ${\ensuremath{\ell}}_{(\mathrm{VLTI})}\ensuremath{\lesssim}1.6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\text{ }\text{ }\mathrm{AU}$ (at 68% confidence level), respectively.