Geodesic dynamics and tidal forces in a quantum-regularized black hole from string T-duality

Abstract

In this work, we investigate the geodesic dynamics and tidal force effects in neutral and electrically charged regular spacetimes inspired by T-duality. We first analyze the geometric properties of these solutions, including their regular central structure and horizon configurations, and show how the interplay between the T-duality scale $\ell_0$ and the electric charge $Q$ determines the transition between black hole and horizonless geometries. We then study the motion of massive and massless particles through the corresponding effective potentials, examining the existence and stability of circular orbits and the behavior of their characteristic radii. We further investigate the tidal forces experienced by observers in radial free fall, focusing on the behavior of the radial and angular components, their extrema and sign changes, and the location of these characteristic points relative to the horizon structure of the geometry. We show that the T-duality regularization renders the tidal forces finite in the central region and gives rise to different stretching and compression regimes, including a region of simultaneous compression in both the radial and angular directions, while the electric charge modifies the strength and location of these tidal features. Finally, we analyze the evolution of the geodesic deviation vector for two sets of initial conditions. We find that both the T-duality scale and the electric charge tend to suppress the accumulated radial stretching, whereas the angular deformation is considerably less sensitive to the charge. These results show how the quantum regularization induced by T-duality and the presence of electric charge modify the orbital dynamics and tidal response of these geometries in the strong-field regime. Furthermore, we demonstrate that the corresponding classical limits are recovered appropriately.