On the pair-particle distribution in an imperfect Bose gas

D. ter Haar

Timothy C. Padmore

A. Isihara, D. D. H. Yee

V. A. Gergel’, Rudolf F. Kazarinov, Robert A. Suris

of the behavior of a slightly imperfect Bose gas in a field of randomly distributed impuri­ties 1s cons1dered. The effect of the impurity atoms on the ground state of the system is determined and found to reduce to a local change in the density of the condensate near the impurity atoms. The spectrum a_nd attenuation of one-particle excitations are calculated. The spectrum of the long wavelength excita­

D. ter Haar

Robert H. Kraichnan

The nature of the Einstein-Bose condensation in an imperfect boson gas is discussed. It is argued that no matter how low the temperature, provided it is not zero, macroscopic second-sound waves should be weakly excited as thermal fluctuations about equilibrium. This implies that the single-particle momentum distribution must be smeared so that the state of zero momentum cannot contain a finite fraction of the particles. A microscopic mechanism which independently leads to a momentum spread is discussed. It is suggested that the actual Einstein-Bose condensation of an imperfect gas takes place in energy rather than momentum but that even in terms of this variable it becomes perfectly sharp only at zero temperature. This hypothesis is formulated analytically in terms of correlation functions of the second-quantized boson field.