Speaker
Andrew Lucas
(Stanford University)
Description
Quantum chaos describes the dynamics of a many-body system
at the onset of thermalization, while hydrodynamics
describes the late time dynamics after thermalization has
occurred locally. Consistency between these two
descriptions provides constraints linking hydrodynamic data
such as diffusion constants and sound speeds to quantum
chaos. I will show that in large N quantum field theories,
hydrodynamic coefficients are bounded by a light cone
velocity: the speed at which the region where quantum
scrambling has just begun expands. Under certain
circumstances, including small N, this light cone velocity
can be replaced by the butterfly velocity: the speed at
which the region where quantum information has completely
scrambled expands. Using these bounds I will predict two
unexpected features of holographic models: (i) the
inequivalence of light cone and butterfly velocities in many
theories; (ii) the breakdown of the hydrodynamic gradient
expansion at very long wavelengths in certain charge neutral
plasmas.
