Harmonic chain with velocity flips: thermalization and kinetic theory

TL;DR

This paper investigates the detailed correlation structure and first-order corrections in harmonic chains with velocity flips during heat relaxation, validating kinetic theory predictions with explicit calculations.

Contribution

It derives explicit first-order correlation corrections and revises kinetic theory to accurately describe the thermalization process in harmonic chains.

Findings

Explicit form of first-order corrections to correlations.

Validation of phonon Boltzmann equation predictions.

Identification of correction sources as current-related and eigenbasis changes.

Abstract

We consider the detailed structure of correlations in harmonic chains with pinning and a bulk velocity flip noise during the heat relaxation phase which occurs on diffusive time scales, for $t=O(L^2)$ where $L$ is the chain length. It has been shown earlier that for non-degenerate harmonic interactions these systems thermalize, and the dominant part of the correlations is given by local thermal equilibrium determined by a temperature profile which satisfies a linear heat equation. Here we are concerned with two new aspects about the thermalization process: the first order corrections in $1/L$ to the local equilibrium correlations and the applicability of kinetic theory to study the relaxation process. Employing previously derived explicit uniform estimates for the temperature profile, we first derive an explicit form for the first order corrections to the particle position-momentum correlations. By suitably revising the definition of the Wigner transform and the kinetic scaling limit we derive a phonon Boltzmann equation whose predictions agree with the explicit computation. Comparing the two results, the corrections can be understood as arising from two different sources: a current-related term and a correction to the position-position correlations related to spatial changes in the phonon eigenbasis.