Suppression of long-time anomalies in simple classical liquids

The spectrum of the velocity-autocorrelation function at small frequencies is evaluated within mode-coupling theory for liquid argon at the triple point and for liquid rubidium. We investigate the dynamical processes limiting the asymptotic range over which the low-frequency square-root cusp of the spectrum can be observed. The frequency dependence of the shear viscosity is shown to have the largest effect upon the suppression of the anomalous long-time decay of velocity correlations. Our results indicate that in the high-density fluids considered the above anomaly shows up only as a percent contribution to the spectrum below some 10¹¹ sec^-1.