  The study of the effects of the density variations on the vibrational
dynamics in vitreous silica is presented. A detailed analysis of the dynamical
structure factor, as well as of the current spectra, allows the identification
of a flattened transverse branch which is highly sensitive to the density
variations. The experimental variations on the intensity and position of the
Boson Peak (BP) in v-SiO2 as a function of density are reproduced and
interpreted as being due to the shift and disappearance of the latter band. The
BP itself is found to correspond to the lower energy tail of the excess states
due to the piling up of vibrational modes at energies corresponding to the
flattening of the transverse branch.
