HET Journal club: Koenraad Schalm

Speaker: Koenraad Schalm

Title: (Quantum) Chaos, hydrodynamics and  black hole scrambling

Abstract: A concrete definition of chaos in quantum systems is a regime of exponential growth in a specific out-of-time-ordered correlator. We study this OTOC both in weakly coupled and in strongly coupled theories. In strongly coupled quantum theories with a holographic dual this OTOC is directly related to probing the system's hydrodynamic sound modes. The information contained in the OTOC is dual to a gravitational shock wave and this can be reconstructed in terms of purely diffusion-like gravitational waves at the horizon of a single-sided black hole with specific regularity-enforced imaginary values of frequency and momentum. The fact  that late-time equilibration and early-time chaos are controlled by the same dynamics is also a property of classical dilute gases. For weakly coupled systems, we show that the information contained in the OTOC follows from a Boltzmann kinetic equation for total energy exchange.