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

[Mihailo Čubrović]

Reminder for those interested:

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).

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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