INTERPRETATION OF THE LOW DAMPING OF SUBTHERMAL CAPILLARY WAVES (RIPPLONS) ON SUPERFLUID HE-4

The problem of ripplon damping on superfluid He-4 is reexamined to sho w how imposing the boundary condition constraint at the perturbed rath er than unperturbed surface position results in strong cancellation of the previous result for the three-ripplon interaction. This has order s of magnitude consequences for the relaxation rate of subthermal ripp lons, which is shown to be dominated instead by ripplon-phonon scatter ing proportional to qT(4), in excellent quantitative agreement with re cent experiments.