  New inelastic X-ray scattering experiments have been performed in liquid
lithium at two different temperatures: T=475 K (slightly above the melting
point) and 600 K. Taking advantage of the absence of any kinematical
restriction and incoherent contribution, and pushing the instrumental
resolution up to 1.5 meV, it was possible to perform an accurate investigation
of the dynamic structure factor S(Q,E) in the wavevector range from 1 to 110
nm^-1. For Q smaller than Q_m=25 nm^-1, the position of the main peak of the
static structure factor, a detailed analysis of the lineshapes shows that any
picture of the relaxation mechanisms based on a simple viscoelastic model must
be abandoned. All the spectral features can instead satisfactorily be accounted
for by including both fast and slow relaxation processes. The physical origin
of the slow relaxation is associated to the structural rearrangement, while the
local nature of the fast one is extensively discussed. At larger Q values a
gradual crossover from the strongly correlated to single particle dynamics
occurs, with an important weight provided by quantum effects.
