  We report high-resolution inelastic x ray scattering measurements of the
acoustic phonons of URu2Si2. We observe minimal change in the phonon structure
upon entering the Hidden Order phase. At all temperatures, the longitudinal
acoustic phonons are anomalously broad at low q. There is no evidence to
suggest that the increase in thermal conductivity in the Hidden Order phase is
driven by a change in phonon dispersions or lifetimes. A more likely
explanation is that the magnetic excitations in the Hidden Order state
contribute to thermal transport.
