Generalized hydrodynamics of binary liquids: transverse collective modes

The parameter-free generalized collective modes approach in eight-variable approximation is applied for investigation of transverse dynamics of Lennard-Jones liquid Kr-Ar beyond the hydrodynamic region. We find four branches of propagating eigenmodes in the spectrum of transverse collective excitations. Different basis sets of dynamical variables are applied to estimate the origin of different branches in the spectrum. It is shown that for large wave numbers the general feature of transverse collective excitations is their "partial" character, while in hydrodynamic limit they are formed by collective behavior of liquid. A detailed analysis of the separated contributions from different collective modes into time correlation functions and spectral functions is performed. The condition of existence of high-frequency mass-concentration waves is derived. It is shown that high-frequency collective excitations, caused by the mass-concentration fluctuations, reflect some properties of optic phonon modes in solids.