Dynamics of the energy center of a long-wave low-amplitude disturbance in an anharmonic one-dimensional lattice

The dynamics of a disturbance with finite energy in an infinite monatomic nonlinear one-dimensional lattice are analyzed. Based on the energy dynamics approach proposed earlier, we focus on such disturbance spatial characteristic as the position of its energy center. Restricting our analysis to long-wave low-amplitude disturbances, we investigate the dynamics of the α-FPU chain using its continuous version described by the KdV equation. We establish a connection of the Lagrangian and the energy of the original chain with the two conserving quantities of the KdV equation. Using these two quantities and the known properties of the KdV equation, we propose a method for determining the velocity of the energy center of the disturbance at large times based on the initial conditions.