Overdamped sine-Gordon kink in a thermal bath

TL;DR

This paper investigates the diffusion behavior of sine-Gordon kinks at finite temperature in an overdamped regime, deriving analytical expressions for the diffusion coefficient and validating them with numerical simulations.

Contribution

It provides a perturbative analytical framework for kink diffusion at finite temperature, including temperature-dependent corrections, and compares these with numerical results.

Findings

Diffusion coefficient is linear and quadratic in temperature.

Quadratic temperature dependence arises from phonon interactions.

The width of the wave function grows as the square root of time.

Abstract

We study the sine-Gordon kink diffusion at finite temperature in the overdamped limit. By means of a general perturbative approach, we calculate the first- and second-order (in temperature) contributions to the diffusion coefficient. We compare our analytical predictions with numerical simulations. The good agreement allows us to conclude that, up to temperatures where kink-antikink nucleation processes cannot be neglected, a diffusion constant linear and quadratic in temperature gives a very accurate description of the diffusive motion of the kink. The quadratic temperature dependence is shown to stem from the interaction with the phonons. In addition, we calculate and compute the average value $<\phi(x,t)>$ of the wave function as a function of time and show that its width grows with $\sqrt{t}$. We discuss the interpretation of this finding and show that it arises from the dispersion of the kink center positions of individual realizations which all keep their width.