Theoretical analysis of neutron and X-ray scattering data on He-3

TL;DR

This paper provides a microscopic theoretical explanation for neutron and X-ray scattering data on liquid He-3, showing that observed excitations are within the particle-hole continuum and aligning well with experimental results.

Contribution

It extends the theory of excitations in Fermi fluids to explain high momentum transfer data in He-3, incorporating pair fluctuations beyond RPA.

Findings

High momentum excitations lie inside the particle-hole continuum.

Pair fluctuations sharpen the collective mode.

Theoretical results agree well with experimental data after convolution.

Abstract

X-ray scattering experiments on bulk liquid He-3 have indicated the possibility of the existence of a sharp collective mode at large momentum transfers. We address this issue within a manifestly microscopic theory of excitations in a Fermi fluid that can be understood as proper generalization of the time-honored theory of Jackson, Feenberg, and Campbell of excitations in He-4. We show that both neutron and X-ray data can be well explained within a theory where the high momentum excitations lie in fact inside the particle-hole continuum. "Pair fluctuations" contribute a sharpening of the mode compared to the random phase approximation (RPA). When the theoretical results are convoluted with the experimental resolution, the agreement between theory and X-ray data is quite good.