Energy carriers in the Fermi-Pasta-Ulam $\beta$ lattice: Solitons or Phonons?

TL;DR

This paper investigates energy transport in the Fermi-Pasta-Ulam β lattice, demonstrating that energy carriers are better described as effective phonons rather than solitons based on numerical analysis of propagating fronts.

Contribution

It provides numerical evidence that effective phonons, not solitons, dominate energy transport in the FPU β lattice, clarifying the nature of energy carriers.

Findings

Effective phonons match numerical data for energy carriers.

Solitons do not align with the observed energy transport.

Strong evidence supports phonons over solitons as energy carriers.

Abstract

We investigate anomalous energy transport processes in the Fermi-Pasta-Ulam $\beta$ lattice. They are determined by the maximum sound velocity of the relevant weakly damped energy carriers. That velocity can be numerically resolved by measuring the propagating fronts of the correlation functions of energy/momentum fluctuations at different times. The numerical results are compared with the predictions for solitons and effective (renormalized) phonons, respectively. Excellent agreement has been found for the prediction of effective long wavelength phonons, giving strong evidence that the energy carriers should be effective phonons rather than solitons.