One-Phonon Spectral Function for Solid Helium

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Abstract
Approximate numerical calculations are used in order to understand some of the differences in size and shape of secondary structure obtained in calculations of the one-phonon spectral function for solid helium that have been reported in the literature. It is seen that Horner's self-consistent treatment of the bubble diagram significantly increases the size of such structure over that obtained in perturbative calculations such as used by Glyde and co-workers. A computational procedure used by Horner in evaluating the spectral function may also further enhance the appearance of secondary peaks in the tail region. Previous explanations of these secondary peaks are reviewed and criticized. Other calculations of the one-phonon spectral functions for the solid heliums are briefly discussed.