Time: 10:00-12:00, June 23, 2026

Location: Seminar Room of KITS, UCAS

Speaker: Surojit Dalui (Shanghai Univ.)

Abstract:

We study classical chaotic dynamics of bounded massless particle motion in Reissner Nordström and Kerr black hole spacetimes across the transition from non extremal to exactly extremal configurations. The surface gravity of a non extremal horizon provides a natural horizon time scale that also appears in shockwave and out of time ordered correlation function descriptions of quantum scrambling. Our calculation instead follows the divergence of nearby classical trajectories in phase space. Using Lyapunov exponents and phase space diagnostics, we examine how the classical instability changes with charge and rotation and compare near extremal and exactly extremal cases. We find that the dynamics at exact extremality is not captured by a naive continuation of the non extremal surface gravity benchmark. This reflects the qualitative change in the near horizon geometry at extremality. The results show that classical orbital chaos provides a useful probe of the non smooth extremal limit, while remaining distinct from a direct calculation of the quantum chaos exponent.