Theory and data analysis for excitations in liquid $^4$He beyond the   roton minimum
  The hybridization of the single-excitation branch with the two-excitation continuum in the momentum region beyond the roton minimum is reconsidered by including the effect of the interference term between one and two excitations. Fits to the latest experimental data with our model allow us to extract with improved accuracy the high momentum end of the $^4$He dispersion relation. In contrast with previous results we find that the undamped excitations below two times the roton energy survive up to Q=3.6 A^{-1} due to the attractive interaction between rotons. 
F. Pistolesi (Institut Laue-Langevin, Grenoble, France)