High-Momentum-Transfer Neutron-Liquid-Helium Scattering and Bose Condensation.

MANFRED L. RISTIG, P. M. Lam, J. W. Clark

Dmitriy Baranov, Zh. A. Kozlov, L. Siurakshina +1 more

The spectrum of noncondensate excitations in neutron scattering on bosons is obtained in the framework of the Bogoliubov models both for liquid 4He and a dilute gas. The problem is solved using a path-integral representation of the partition function of the system. We describe the influence of scattering of neutrons on a Bose condensate in a stationary (time-independent) picture in the Gibbs equilibrium ensemble. This influence is a stationary boson response, and it depends on the initial neutron momentum k, transfer momentum p, and the neutron-boson interaction λ, which is related to the scattering length. The contribution of the neutrons to the initial Bogoliubov spectrum is found to be important for “quasi-elastic” scattering on the noncondensate, while the contribution of deep inelastic scattering is small; no contribution from elastic scattering on the Bose condensate is found. In the case of liquid Helium, the response is unlikely to be observable for all values p. On the other hand, for a gas one may expect a visible effect, in particular for a small momentum transfer p and a small density of the Bose condensate ϱ.

Allan Griffin

Dmitriy Baranov, Zh. A. Kozlov, L. Siurakshina +1 more

Abstract The spectrum of noncondensate excitations in neutron scattering on bosons is obtained in the framework of the Bogoliubov models both for liquid 4 He and a dilute gas. The problem is solved using a path‐integral representation of the partition function of the system. We describe the influence of scattering of neutrons on a Bose condensate in a stationary (time‐independent) picture in the Gibbs equilibrium ensemble. This influence is a stationary boson response, and it depends on the initial neutron momentum k , transfer momentum p , and the neutron‐boson interaction λ, which is related to the scattering length. The contribution of the neutrons to the initial Bogoliubov spectrum is found to be important for “quasi‐elastic” scattering on the noncondensate, while the contribution of deep inelastic scattering is small; no contribution from elastic scattering on the Bose condensate is found. In the case of liquid Helium, the response is unlikely to be observable for all values p . On the other hand, for a gas one may expect a visible effect, in particular for a small momentum transfer p and a small density of the Bose condensate ϱ.

Bipin R. Desai

Joseph Jacob Weinstein, John W. Negele

Scaling of the dynamic structure factor at high momentum transfer is established by using time-ordered perturbation theory. Whereas the scaling function is the longitudinal momentum distribution for systems interacting with smooth two-body potentials, additional terms contribute in the case of strong short-range repulsion. Illustrative results are presented for a hard-sphere Bose gas and the relevance to electron scattering from nuclei and neutron scattering from liquid helium is discussed.