Excitations of liquid 4He in disorder

We discuss the effect of disorder and confinement on the excitations in superfluid and normal liquid He-4. Neutron scattering measurements of the excitations to date are limited to helium in aerogel. There the phonon-roton energy and width are slightly modified by disorder but there is no evidence for additional excitations at low energy nor of a gap in the phonon energy at long wavelengths. Experimental difficulties are discussed. In a recent path-integral Monte-Carlo study, in which a high density of point impurities are introduced at random positions, a significant broadening and energy shift are found together with additional lour-energy excitations. PACS numbers: 67.40.-w.