1. T. Worthington, J. Yan, and J. U. Trefny,J. Low Temp. Phys. 22, 293 (1976).
2. I. M. Khalatnikov,An Introduction to the Theory of Superfluidity (Benjamin, New York, 1965), Part II, and references therein.
3. L. D. Landau,J. Phys. USSR 5, 71 (1941).
4. I. M. Khalatnikov and D. M. Chernikova,Zh. Eksp. Theor. Fiz. 50, 411 (1966) [English transl.,Sov. Phys. ? JEPT 23, 274 (1966)], and references therein.
5. B. M. Abraham, Y. Eckstein, J. B. Ketterson, M. Kuchnir, and P. R. Roach,Phys. Rev. A 1, 250 (1970).