Breathers in FPU systems, near and far from the phonon band
  There exists a recent mathematical proof on the existence of small amplitude breathers in FPU systems near the phonon band, which includes a prediction of their amplitude and width. In this work we obtain numerically these breathers, and calculate the range of validity of the predictions, which extends relatively far from the phonon band. There exist also large amplitude breathers with the same frequency, with the consequence that there is an energy gap for breather creation in these systems. 
B. Sanchez-Rey, J.F.R. Archilla, G. James, and J. Cuevas