Fig. 3.

Spectroscopic parameters calculated from the dynamic structure factors $S_T\left(\overrightarrow{q},\omega \right)$. (A) Transverse phase velocity, $c_{T_2}\left(\mathrm{\Omega }\right)={\mathrm{\Omega }}_{T_2}\left(q\right)/q$, and (B) broadening, ${\mathrm{\Gamma }}_{T_2}\left(\mathrm{\Omega }\right)$, for the T₂ excitations at the indicated values of λ. These data have been obtained by fitting the calculated $S_T\left(\overrightarrow{q},\omega \right)$ to the damped harmonic oscillator line shape of Eq. 2. The horizontal dashed line in A corresponds to the macroscopic limit of the sound velocity at λ = 0.7. The dashed lines ∝ Ω² and ∝ Ω⁴ in B are also guides for the eye, to emphasize the extremely complex frequency dependence of ${\mathrm{\Gamma }}_{T_2}$ at different values of λ. A comprehensive discussion of these data is included in the text.