Sudden interaction quench in the quantum sine-Gordon model

TL;DR

This paper investigates the non-equilibrium dynamics of the quantum sine-Gordon model after a sudden interaction quench, revealing a universal factor-two relaxation in mode occupation numbers in the weak-coupling regime.

Contribution

It introduces a flow equation method to analyze real-time dynamics and identifies a universal non-thermal relaxation feature in the weak-coupling quantum sine-Gordon model.

Findings

Mode occupation numbers relax to twice their equilibrium values

Universal non-thermal distribution observed in weak-coupling regime

Weak-coupling quantum sine-Gordon model is on the borderline between thermalization and non-thermalization

Abstract

We study a sudden interaction quench in the weak-coupling regime of the quantum sine-Gordon model. The real time dynamics of the bosonic mode occupation numbers is calculated using the flow equation method. While we cannot prove results for the asymptotic long time limit, we can establish the existence of an extended regime in time where the mode occupation numbers relax to twice their equilibrium values. This factor two indicates a non-equilibrium distribution and is a universal feature of weak interaction quenches. The weak-coupling quantum sine-Gordon model therefore turns out to be on the borderline between thermalization and non-thermalization.