Excitation Energy of Liquid Helium. II

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Abstract
The excitation spectrum of liquid Helium II is re-examined using the formalism developed by Sunakawa et al. In this formalism, certain divergent terms appear—a constant term and the terms involving products of two field operators. We show that it is necessary to retain them in order to obtain convergent results in pertubation calculations. Results for the energy spectrum and structure factor are derived in perturbation theory and are thus shown to be convergent in contrast to the earlier observations by Sunakawa et al. to the contrary. Similar corrections are also derived for the temperature dependent formalism developed recently by Kebukawa. The new expression for the excitation energy is numerically evaluated in such a way as not to depend on model interatomic potentials and is found only to be in fair agreement with experimental result.

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