Entanglement and fast quantum thermalization in heavy ion collisions

Abstract

Let [Formula: see text] be subsystem of a larger system [Formula: see text] and [Formula: see text] be a typical state from the subspace of the Hilbert space [Formula: see text] satisfying an energy constraint. Then [Formula: see text] is nearly thermal. We discuss how this observation is related to fast thermalization of the central region ([Formula: see text]) in heavy ion collisions (HIC), where [Formula: see text] represents other degrees of freedom (soft modes, hard jets, collinear particles) outside of [Formula: see text]. Entanglement between the modes in [Formula: see text] and [Formula: see text] play a central role: the entanglement entropy [Formula: see text] increases rapidly in the collision. In gauge–gravity duality, [Formula: see text] is related to the area of extremal surfaces in the bulk, which can be studied using gravitational duals.