Weak gravitational lensing in Ricci-coupled Kalb–Ramond bumblebee gravity: Global monopole and axion-plasmon medium effects

In this paper, we study the influence of the axion-plasmon medium, as proposed in [10.1103/PhysRevLett.120.181803] Terças et al. (2018), on the optical properties of black holes in a Lorentz-violating spacetime containing a global monopole. Our primary aim is to provide a test for detecting the effects of a fixed axion-plasmon background within the framework of Ricci-coupled Kalb–Ramond bumblebee gravity. By extending the conventional Einstein–bumblebee model through a nonminimal coupling between the Kalb–Ramond field and the Ricci tensor, we demonstrate that the combined presence of a global monopole and Lorentz-violating effects induces significant modifications to the classical Schwarzschild lensing signature. Employing the Gauss–Bonnet theorem within an optical geometry approach, we derive an analytical expression for the deflection angle that incorporates both linear and quadratic contributions from the Lorentz-violating parameter and the monopole charge. Furthermore, we investigate how the axion-plasmon coupling alters light propagation, affecting key observable gravitational deflection angle. Our results indicate that these optical characteristics are notably sensitive to the axion-plasmon parameters, thereby offering promising observational signatures for probing new physics beyond standard general relativity.