Critical dynamics of theλtransition in liquidHe4: Light-scattering spectrum

From kinetic-theory considerations a general expression is derived for the frequency-dependent critical thermal conductivity of liquid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ near its $\lambda$ point. Adding the transient solutions yields an expression for the temperature- and frequency-dependent entropy relaxation rate which includes the corrections to dynamic scaling. This is used to study the fluctuation spectrum at and above the $\lambda$ point. A detailed comparison with the light scattering data of Tarvin, Vidal, and Greytak yields good agreement.