Evidence of two viscous relaxation processes in the collective dynamics ofliquid lithium

New inelastic x-ray scattering experiments have been performed on liquid li thium in a wide wave vector range. With respect to the previous measurement s, the instrumental resolution, improved up to 1.5 meV, allows one to accur ately investigate the dynamical processes determining the observed shape of the dynamic structure factor S(Q, omega). A detailed analysis of the line shapes shows the coexistence of relaxation processes with both slow and fas t characteristic time scales, and therefore shows that pictures of the rela xation mechanisms based on a simple viscoelastic model must be abandoned.