Title: Kinetic relaxing processes in collective dynamics of pure liquids
Authors: T.Bryk, I.Mryglod (Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, 1 Svientsitskii Str., 79011 Lviv, Ukraine)

The role of nonhydrodynamic relaxing processes in collective dynamics of pure liquids is studied within a generalized collective modes approach. A five-variable model of generalized hydrodynamics is solved analytically in long-wavelength limit. Among five collective modes we found three hydrodynamic and two relaxing kinetic excitations. Two latter ones describe the viscous and heat relaxation in liquid. A comparison of analytical results and molecular dynamics data is performed for a Lennard-Jones fluid and a liquid metal. A crossover from standard hydrodynamics to molecular regime in relaxational behaviour of simple liquids is discussed.

Key words: generalized hydrodynamics, collective excitation, dynamical structure factor, relaxation processes
PACS: 05.20.Jj,61.20.Ja,61.20.Lc