У оквиру Семинара о струнама, холографији и хаосу, у среду, 28. јануара 2026. године у 12 часова у сали 360 Института за физику у Београду, др Димитриос Гијатаганас (Национални центар за теоријсксе науке, Тајпеј, Тајван) одржаће предавање:
Photon Rings and Holography: A Unified View from the Penrose Limit
САЖЕТАК:
The unstable circular photon orbits around black holes encode rich information about the geometry and dynamics of spacetime. In the high-frequency limit, the eikonal quasinormal modes of a black hole are
intimately connected to the exponential divergence of these circular photon orbits. We present an alternative geometric derivation of this correspondence by employing the Penrose limit, which captures the physics near the photon ring. The resulting plane wave geometry reveals a direct link between the frequency matrix of the massless wave equation which takes the form of an inverted quantum harmonic oscillator, and the instability of null geodesics and their associated Lyapunov exponents. Remarkably, the Lyapunov exponents, orbital frequencies, and quasinormal mode spectrum can all be derived from a single Hamiltonian defined in the Penrose limit geometry. As an application, we discuss how our framework may serve as a foundation for a holographic dual description of astrophysical black holes, with the photon ring emerging as an effective holographic horizon and how Lyapunov exponents are subject to fundamental upper bounds.