Neutron Scattering from LiquidHe3

The dynamical form factor $S(Q,\omega )$ of liquid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$, including both the coherent and the incoherent contributions, is calculated within the random-phase approximation. At low temperature a sharp zero-sound mode is obtained. At higher temperature this mode becomes a broad resonance in the particle-hole spectrum. This temperature effect may help account for the difference in $S(Q,\omega )$ observed in two recent neutron-scattering experiments.