Attenuation of the fourth sound in liquid helium II via extended thermodynamics

This work continues a study begun in previous works, where a non-standard model of liquid helium II is proposed, in which a small entropy transfer is associated with the superfluid component. In this work the influence of this superfluid entropy on the propagation of the fourth sound is analyzed. From experimental data for velocities and attenuations of the first and second sound, the model provides speed and attenuation coefficient of the fourth sound in a porous medium as a function of the ratio s_s/s between the superfluid entropy s_s and the total entropy s. These values are determined in the two limiting cases s_s/s=0 and =0.02, for various values of temperature and pressure.