Theory of Acoustic Impedance of Superfluid 3He

A microscopic theory of transverse acoustic impedance of superfluid 3He at low temperatures is presented. we calculate the stress tensor of superfluid 3He as a response to the oscillating rough wall. For that purpose, we extend a quasi-classical theory based on the random S-matrix model to time dependent problems. We show that by virtue of the pair breaking mechanism the transverse impedance can be finite even at T=0 K. This is in contrast to the theories using the quasi-particle distribution function which predict that the impedance tends to zero like a Yosida function.