Three-phonon relaxation in isotropic and anisotropic phonon systems of liquid helium at different pressures

Starting from the kinetic equation for phonons in superfluid helium, expressions for the rates of three-phonon scattering in isotropic and anisotropic phonon systems are obtained for different pressures. These expressions are valid in the whole range of energies where three-phonon processes are allowed. Limiting cases are analyzed and compared with the results of previous theoretical investigations. The obtained pressure and angular dependence of three phonon scattering rate allows one to explain the experimental data on interaction of phonon pulses. (C) 2005 American Institute of Physics.