[40] G. Bertaina, L. Pitaevskii, and S. Stringari, arXiv:1002.0195. [41] E. M. Lifshitz and L. P. Pitaevskii, Statistical Physics, Part 2 (Butterworth-Heinemann, Oxford, 2002). [42] B. M. Abraham, Y. Eckstein, J. B. Ketterson, M. Kuchnir, and P. R. Roach, Phys. Rev. A 1 , 250 (1970). [43] I. M. Khalatnikov, Introduction to the theory of superfluidity , (W. A. Benjamin, N.Y., 1965). [44] With a better theory of the thermodynamics than NSR, we would find that δ diverges at T = T$_{c}$ (as it does in superfluid $^{4}$He). Our point here is that it is also significant in a large region below T$_{c}$ . 33