Spectral functions in nuclear matter

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Abstract
Spectral functions are calculated from mean fields calculated both by Brueckner and by Botermans-Malfliet Green’s function methods. Similarities and differences between the two methods are illustrated. Results are shown at normal nuclear matter density and zero temperature. Calculations are made by the separable phase-shift technique that was introduced earlier including the single-particle strength up to ∼1700 MeV with (usually) less than 1% of the total strength missing. It is found that ∼5% of the single particle strength lies above 500 MeV. Mean removal (centroid) energies of nucleons and occupation numbers are calculated by energy averaging over the spectral functions. The averages are also done in the extended quasiparticle approximation for the spectral function discussed in an earlier paper showing good agreement with the ‘‘exact’’ results. It is in fact shown that this approximation yields the same result for centroid energies as does Koltun’s work which was based on an analysis of the linked cluster expansion. The total energy is calculated by Koltun’s sum rule which involves an integration over the calculated (correlated) occupation numbers. The result compares favorably with the Brueckner energy which involves an integration over model (uncorrelated) occupation numbers.