On the mutual polarization of two He-4 atoms

We propose a simple method based on the standard quantum-mechanical perturbation theory to calculate the mutual polarization of two atoms He^4.Comment: 9 pages, 1 table; the article is revised and the calculation is essentially refined; v4: final version, the Introduction is delete

Theory of a Narrow roton Absorption Line in the Spectrum of a Disk-Shaped SHF Resonator

We calculate the probability of the birth of a circular phonon (c-phonon) in He II by a c-photon of the resonator. It is shown that this probability has sharp maxima at frequencies, where the effective group velocity of the c-phonon is equal to zero; the density of states of c-phonons strongly grows at such frequencies. For He II, these frequencies correspond to a roton and a maxon. From the probability of the c-roton birth, we calculate the roto line width which is found to approximately agree with the experimental one. We conclude that the roton line observed in the super-high-frequency (SHF) absorption spectrum of helium is related to the birth of c-rotons. A possible interpretation of the Stark effect observed for the roton line is also proposed.Comment: 13 pages, 1 figure, v2: journal variant, several minor correction

Possible experiment for determination of the role of microscopic vortex rings in the \lambda-transition in He-II

It is suggested that microscopic vortex rings (MVR) play an important role in the \lambda-transition in helium-II and substantially determine the value of T_{\lambda}. For very thin films of He-II, with thickness d less than the size of the smallest MVR, the rings do not fit in and, therefore, do not exist in such films. Consequently, for superfluid films of He-II, a peculiarity in the form of a smoothed-out jump should be observed in the curve T_{m}(d) at the values of thickness approximately equal to the size of the smallest MVR, d= 3 - 9 A (T_{m} is the temperature of the maximum of the broad peak on the curve of the dependence of the specific heat on temperature). The absence of a similar peculiarity will be an evidence that MVR do not influence the values of T_{\lambda} and T_{m}, and do not play any key role in the \lambda-transition. The currently available experimental data are insufficient for revealing the predicted peculiarity.Comment: 6 pages, 2 figure