Solidity of viscous liquids. III: Alpha relaxation

It is suggested that the omega^{-1/2} high-frequency decay of the alpha loss in highly viscous liquids, which appears to be generic, is a manifestation of a negative long-time tail as typically encountered in stochastic dynamics. The proposed mechanism requires that the coherent diffusion constant is much larger than estimated from the alpha relaxation time. This is shown to follow from the solidity of viscous liquids in an argument which, utilizing the irrelevance of momentum conservation at high viscosity, predicts that at high viscosity the coherent diffusion constant is much larger than the incoherent diffusion constant.