Role of quantum fluctuations in a system with strong fields: Onset of hydrodynamical flow

TL;DR

This paper investigates how quantum fluctuations influence the transition to hydrodynamical behavior in a scalar field model with strong external sources, shedding light on thermalization processes relevant to heavy ion collisions.

Contribution

It demonstrates that resumming quantum fluctuations leads to hydrodynamical evolution in a scalar field model, providing insights into thermalization in high-energy nuclear physics.

Findings

Quantum fluctuations cause the system to follow ideal hydrodynamics.

Resummation of secular quantum terms is essential for accurate evolution.

Results suggest a pathway to understanding thermalization in gauge theories.

Abstract

Quantum fluctuations are believed to play an important role in the thermalization of classical fields in inflationary cosmology but their relevance for isotropization/thermalization of the classical fields produced in heavy ion collisions is not completely understood. We consider a scalar $\phi^4$ toy model coupled to a strong external source, like in the Color Glass Condensate description of the early time dynamics of ultrarelativistic heavy ion collisions. The leading order classical evolution of the scalar fields is significantly modified by the rapid growth of time-dependent quantum fluctuations, necessitating an all order resummation of such "secular" terms. We show that the resummed expressions cause the system to evolve in accordance with ideal hydrodynamics. We comment briefly on the thermalization of our quantum system and the extension of our results to a gauge theory.