[hep-th] Strings, Holography & Chaos Seminar January 28 12:00 CET (IPB, 2nd floor theory seminar room): Dimitrios Giataganas

[Mihailo Čubrović]

Dear friends,

On January 28 (Wednesday) at 12:00 CET we will have a seminar by 
Dimitrios Giataganas, in the theory seminar room (Institute of Physics 
Belgrade, 2nd floor). Dimitrios will be around most of the time from 
Monday to Friday next week, so if you want to have a chat there will be 
plenty of time; drop me an email and I'll get you in touch. Title and 
abstract follow.

Photon Rings and Holography: A Unified View from the Penrose Limit

Dimitrios Giataganas, National Center for Theoretical Sciences, Taipei, 
Taiwan


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.



-- 
Dr. Mihailo Čubrović

Center for the Study of Complex Systems
Institute of Physics Belgrade
National Institute of the Republic of Serbia
Pregrevica 118, 11080 Belgrade, Serbia
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