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The method of collective variables (MCV) has been used to calculate thelogarithm of the He-II ground-state wave function, ln(Psi_0), to an accuracy ofa first correction to the Jastrow function and, in a second approximation, thewave function Psi_k of the first excited state and the He-II quasiparticlespectrum. The functions Psi_0 and Psi_k were found as the eigenfunctions of theN-particle Schro"dinger equation, and the function Psi_0 was connected to thestructure factor of He-II, using the Vakarchuk equation. The model does notcontain any fitting parameter or function. The quasiparticle spectrumcalculated numerically agrees well with the experiment. Our solution improvesthe result obtained early by Yukhnovskyi and Vakarchuk.

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