HEP2026: 42nd Conference on Recent Developments in High Energy Physics and Cosmology [NTUA] Jul 8 – 11, 2026

Photon Rings: Universal Penrose Limits and Fast Scrambling

Not scheduled

20m

Main Hall (Level 1) (National Technical University of Athens)

Theory

Speaker

Prof. Dimitrios Giataganas (NCTS)

Description

We investigate the dynamics of unstable null geodesics through the universal Penrose limit of axisymmetric black holes. Utilizing the Killing-Yano tensor, we show how the resulting plane wave geometry directly encodes the instabilities of photon rings, allowing quasinormal modes and Lyapunov exponents to be extracted from a single effective Hamiltonian. We then connect these geometric properties to a fast scrambling instability conjecture in binary black hole mergers. By mapping a quasi-circular binary onto an effective Kerr metric, we demonstrate that the merger's final state naturally maximizes a photon ring's Lyapunov exponent. This suggests a connection between post-merger black hole remnants and the dynamics of unstable null orbits.