SUBSONIC SOLITONS IN THE FERMI-PASTA-ULAM CHAIN

Computer simulations show that in a one-dimensional lattice with quart ic anharmonic localized modes can move with a constant velocity that i s smaller than the sound velocity (subsonic solitons). In this paper w e present an analytical investigation of the wing of the subsonic soli ton, which allows for the calculation of the dispersion relation of th ese modes. The total envelope of the displacement is calculated numeri cally by means of a Gaussian error integral method, and the obtained s olutions are tested via direct numerical simulations. Among many resul ts, it is found that subsonic solitons with velocity very close to the sound velocity are possible.