Cosmological Particle Production at Strong Coupling

TL;DR

This paper investigates how a strongly-coupled quantum field theory behaves in an expanding universe using holography, revealing rapid loss of initial conditions and hydrodynamic evolution during cosmological expansion.

Contribution

It provides the first detailed holographic analysis of particle and entropy production in a strongly-coupled gauge theory during cosmological expansion.

Findings

Strong coupling leads to rapid loss of initial state memory.

Particle production is inseparable from entropy production at strong coupling.

Hydrodynamic behavior emerges when the Hubble parameter is much smaller than the initial temperature.

Abstract

We study the dynamics of a strongly-coupled quantum field theory in a cosmological spacetime using the holographic AdS/CFT correspondence. Specifically we consider a confining gauge theory in an expanding FRW universe and track the evolution of the stress-energy tensor during a period of expansion, varying the initial temperature as well as the rate and amplitude of the expansion. At strong coupling, particle production is inseparable from entropy production. As a result, we find significant qualitative differences from the weak coupling results: at strong coupling the system rapidly loses memory of its initial state as the amplitude is increased. Furthermore, in the regime where the Hubble parameter is parametrically smaller than the initial temperature, the dynamics is well modelled as a plasma evolving hydrodynamically towards equilibrium.