Interpretation of Inelastic Neutron-Scattering Observations in bcc Solid and SuperfluidHe4

Recent inelastic neutron scattering observations on the bcc phase of solid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ are interpreted as showing (i) substantial interference between the one-phonon peak and the multiphonon background, due to strong phonon interaction processes; and (ii) a Debye-Waller factor, extracted by use of first-moment sum rules, which closely resembles the structure of superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. We discuss implications of this resemblance for the ground-state wave functions of crystalline and superfluid helium.