Charged Black Holes in the Kalb-Ramond Background with Lorentz Violation: Null Geodesics and Optical Appearance of a Thin Accretion Disk

Abstract: In this paper, we investigate the optical appearance of a charged black hole in the Kalb-Ramond background, incorporating a Lorentz-violating parameter $l=0.01$. By analyzing the null geodesics, we derive the photon sphere, event horizon, effective potential, and critical impact parameters. We then employ a ray-tracing technique to study the trajectories of photons surrounding a thin accretion disk. Three different emission models are considered to explore the observed intensity profiles of direct rings, lensing rings, and photon sphere. By comparing these results with those of the standard Reissner-Nordstr\"om black hole ($l=0$) and the Kalb-Ramond black hole with different values of Lorentz-violating parameter (specifically, $l=0.05$ and $l=0.1$ respectively), we find that the Lorentz symmetry breaking will lead to a decrease in the radii of the photon sphere, the event horizon, and the innermost stable circular orbit. Consequently, this makes the detection of these black holes more challenging.