Thermalization and Hydrodynamics of Two-Dimensional Quantum Field Theories

TL;DR

This paper establishes a lower bound on the timescale for hydrodynamics onset in 2D quantum field theories, linking causality, universality, and deformation scales, and explores implications for thermodynamics and effective field theories.

Contribution

It introduces a parametric lower bound on hydrodynamization time in 2D QFTs based on causality and universality principles, extending understanding of thermalization.

Findings

Lower bound on hydrodynamics onset timescale

Constraints on the sign of the al Tar term in EFTs

Definition of a thermodynamic C-function

Abstract

We consider 2d QFTs as relevant deformations of CFTs in the thermodynamic limit. Using causality and KPZ universality, we place a lower bound on the timescale characterizing the onset of hydrodynamics. The bound is determined parametrically in terms of the temperature and the scale associated with the relevant deformation. This bound is typically much stronger than $\frac{1}{T}$, the expected quantum equilibration time. Subluminality of sound further allows us to define a thermodynamic $C$-function, and constrain the sign of the $\mathcal T\bar{\mathcal T}$ term in EFTs.