Title: Mechanism of collisionless sound damping in dilute Bose gas with condensate
Author(s):

	Yu. Slyusarenko (Akhiezer Institute for Theoretical Physics, NSC KIPT, 1, Akademicheskaya Str., Kharkov 61108, Ukraine; Karazin National University, 4, Svobody Sq., Kharkiv 61077, Ukraine)
	A. Kruchkov (Karazin National University, 4, Svobody Sq., Kharkiv 61077, Ukraine)

We develop a microscopic theory of sound damping due to Landau mechanism in dilute gas with Bose condensate. It is based on the coupled evolution equations of the parameters describing the system. These equations have been derived in earlier works within a microscopic approach which employs the Peletminskii-Yatsenko reduced description method for quantum many-particle systems and Bogoliubov model for a weakly nonideal Bose gas with a separated condensate. The dispersion equations for sound oscillations were obtained by linearization of the mentioned evolution equations in the collisionless approximation. They were analyzed both analytically and numerically. The expressions for sound speed and decrement rate were obtained in high and low temperature limiting cases. We have shown that at low temperature the dependence of obtained quantities on temperature varies significantly from those one obtained by other authors in the semi-phenomenological approaches. Possible effects connected with non-analytic temperature dependence of dispersion characteristics of the system were also indicated.

Key words: dilute Bose gas, Bose-Einstein condensate (BEC), microscopic theory, sound, Landau mechanism, dispersion relations, speed of sound, damping rate
PACS: 05.30.-d, 05.30.Jp, 67.85.Hj, 67.85.Jk, 03.75.Hh, 03.75.Kk

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