Sound propagation in liquid helium near theλpoint. II. Ultrasonic attenuation

Abstract
We present an improved theory of critical ultrasonic attenuation above the λ point that is in good agreement with the experimental data. Static interactions are taken into account by means of a simple modification of the single-loop specific-heat integral. Dynamic interactions, important in the crossover regime at low frequencies, produce a frequency-dependent change in the kinetic coefficient, without otherwise changing the scaling function.