  The findings of X-ray and neutron scattering experiments on amorphous systems
are interpreted within the framework of the theory of Euclidean random
matrices. This allows to take into account the topological nature of the
disorder, a key ingredient which strongly affects the vibrational spectra of
those systems. We present a resummation scheme for a perturbative expansion in
the inverse particle density, allowing an accurate analytical computation of
the dynamical structure factor within the range of densities encountered in
real systems.
