On the role of quasi-localized soft-mode vibrations in the boson peak and quasi-elastic scattering in glasses

It is argued that the contribution of quasi-localized 1D soft-mode vibratio nal excitations to the photon (neutron) quasi-elastic scattering (QES) corr elated with the boson peak in glasses can be considerable, as well as the e arlier revealed contribution of acoustic phonons is. The main points are th at only anharmonic coupling of the 1D soft mode with acoustic modes can giv e rise to this kind of QES and, at least for direct cubic anharmonic coupli ng, the coupling coefficient in a glass is finite. (C) 1999 Elsevier Scienc e B.V. All rights reserved.