Gap relaxation and its effect on sound attenuation near Tc

Using a linearized Boltzmann equation approach coupled with a generalized gap equation, we calculate the contribution to sound attenuation due to the slow relaxation of the amplitude of the order parameter close to the transition temperature. A peak in the longitudinal sound attenuation is found, the amplitude of which depends crucially on (/EF)2 and the magnitude of the Grüneisen parameter. In heavy-fermion systems this contribution is seen to be substantial and might account for the observed peak in the sound attenuation near Tc.