Calculation of the He-II quasiparticle spectrum by the method of collective variables

TL;DR

This paper employs the method of collective variables to calculate the He-II quasiparticle spectrum, achieving high accuracy without fitting parameters, and improving upon previous theoretical results with good experimental agreement.

Contribution

It introduces a parameter-free, collective variable-based approach to compute the He-II quasiparticle spectrum, enhancing prior theoretical models.

Findings

Numerical quasiparticle spectrum agrees well with experimental data.

The method improves upon earlier theoretical calculations.

The approach does not require fitting parameters or functions.

Abstract

The method of collective variables (MCV) has been used to calculate the logarithm of the He-II ground-state wave function, ln(Psi_0), to an accuracy of a first correction to the Jastrow function and, in a second approximation, the wave function Psi_k of the first excited state and the He-II quasiparticle spectrum. The functions Psi_0 and Psi_k were found as the eigenfunctions of the N-particle Schro"dinger equation, and the function Psi_0 was connected to the structure factor of He-II, using the Vakarchuk equation. The model does not contain any fitting parameter or function. The quasiparticle spectrum calculated numerically agrees well with the experiment. Our solution improves the result obtained early by Yukhnovskyi and Vakarchuk.