Hydrodynamics of the Fermi-Pasta-Ulam-Tsingou chain

Abstract

We provide a pedagogical review of the hydrodynamics of the FPUT chain. There are three hydrodynamic fields corresponding to the conservation of mass, momentum and energy. We provide physically motivated derivations of the hydrodynamic equations at the levels of Euler and then Navier-Stokes-Fourier. Next we consider examples to test as to how successful the hydrodynamic description is in predicting the observed time evolution of nonequilibrium initial conditions such as domain walls and blasts. We find that in some cases there is good agreement of microscopic simulations with predictions from the Euler equations while, in several other cases, there is significant departure from the Euler predictions suggesting that the role of dissipation and noise is important in general.