We discuss a number of unusual phenomena, which have been discovered recently in anisotropic quasiparticle systems in superfluid 4He. These include the creation of high-energy phonons by a pulse of low-energy phonons, the suprathermal distribution of high-energy phonons in long phonon pulses, the mesa shape of the angular distribution of low-energy phonons, the creation of a «hot line» when two-phonon
pulses cross. The thermodynamic properties of anisotropic quasiparticle systems of He II are derived for all degrees of anisotropy.
Adamenko, I.; Nemchenko, K.; Slipko, V.; Wyatt, A. The Unusual Properties of Anisotropic Systems of Quasiparticles in Superfluid 4He. Fiz. Nizk. Temp.2007, 33, 1008-1015.