Regular spherically symmetric solutions in General Relativity and scalar-tensor gravity coupled to nonlinear electrodynamics and their stability

Abstract

We investigate the geometric, dynamical, and thermodynamic properties of a novel class of regular black holes in scalar-tensor gravity non-minimally coupled to nonlinear electrodynamics (NED). By incorporating a purely magnetic NED source within a scalar-tensor framework, we circumvent the classical ``no-go'' theorems. These theorems, strictly formulated for scalar-free Einstein-NED systems, prohibit regular configurations for purely electric fields due to the fundamental requirement of recovering the linear Maxwell limit at spatial infinity. The geometric analysis demonstrates the complete resolution of the central Penrose singularity, replacing it with a regular, globally bounded vacuum core ($|\rho_c| < \infty$). While purely electromagnetic regular black holes canonically possess a de Sitter center, the deep potential well of the scalar field in our model structurally alters this standard geometry, yielding a locally Anti-de Sitter (AdS-like) regime characterized by a strictly negative central energy density ($\rho_c < 0$). To assess the physical viability of these configurations, we analyze their dynamical stability against odd-parity (axial) linear gravitational perturbations. The derived Regge-Wheeler-like effective potential is strictly positive and convex outside the event horizon. Numerical time-domain integration, independently corroborated by the semi-analytical WKB approximation, confirms the total absence of exponentially growing modes, revealing a stable quasi-normal ringing phase followed by an exponential decay. Furthermore, our thermodynamic analysis of the mass-radius relation directly indicates that the semi-classical Hawking evaporation must terminate at the extremal limit ($M = M_{min}$), leaving behind a massive thermodynamic remnant, thereby providing a theoretical framework toward resolving the black hole information loss paradox.