Probing the weak gravity conjecture: Novel Aschenbach signatures in superextremal non-linear charged AdS black holes

Abstract

This study investigates the nonlinear charged Anti-de Sitter (AdS) black hole solution within the framework of massive gravity, motivated by recent advancements linking the Weak Gravity Conjecture (WGC) to phenomena such as Weak Cosmic Censorship Conjecture (WCCC) and photon sphere dynamics. Building on these foundations, we focus on the Aschenbach effect–a relativistic phenomenon intricately tied to the geometry of photon spheres and known to occur in some special sub-extremal non rotating black holes. Our primary objective is to determine whether this effect persists not only up to the extremal limit but also beyond, into the superextremal regime, thus probing the stability and validity of black hole characteristics in these extreme conditions. By analyzing the nonlinear charged AdS black hole solutions in massive gravity, we demonstrate that the Aschenbach effect remains a robust feature across both extremal and superextremal configurations. This extension suggests that key relativistic signatures and the underlying spacetime structures associated with high-spin black holes continue to hold beyond classical boundaries. Our results provide new insights into the behavior of ultra-compact objects and highlight promising directions for exploring the limits of general relativity, as well as potential generalizations of the WGC and WCC in strong gravitational fields.