On the dispersion of the 'roton' second sound in the superfluid helium

At sufficiently high frequencies of the sound when the energy equilibrium between the phonon and roton gases is not established in the superfluid helium there may propagate the second sound through the gas of rotons ('roton' second sound). In the systems of rotons the equilibrium with respect to the number of rotons can be not complete (the chemical protential is not exactly equal to zero). The dispersion of the roton second sound in these conditions is investigated. (Auth.)