Fumiaki Iwamoto

Cluster Expansion of the Ground State of a Bose Particle System

Jastrows variational method was used to obtain an expresston for ground state energy which is very similar to thc expression developed in considerations of a hard-sphere Bose gas at low density. (D.E.B.)

Effect of the Three-Excitation States on the Raman Scattering from Superfluid 4He

Several years ago, OHBAYASHI and UDAGAWA [1] told us that they had seen in the Raman spectrum an abrupt change of the slope at the points a, b, c, d, e, and f as well as peaks at pl and p2.

Theory of Roton-Roton Scattering

Direct observation of roton-roton scattering by Forbes and Wyatt1 is the first example of the scattering between controlled beams of excitations in the condensed matter, and supplies information of elementary processes without thermal average. They found a dramatic increase of the scattering cross section as the probe roton momentum* increases from 2.0 to 2.2A−1.

A Note on the Raman Scattering from Liquid HeII

In the Raman scattering from liquid Hen,,),2) a few elementary excitations are created in the liquid. By confining ourselves to the production of two excitations,3),4) it was shown that the Raman spectrum should have cusps or inflections with infinite derivative at E=2Llo and 2Ll,. Here, E is the energy transferred from the light to the liquid, Llo and Ll, denote the minimum and the maximum energies of the phonon-roton dispersion curve. It is from a specific interference mechanism that the behavior of the spectrum results in spite of the divergence of the density of the produced two-excitation states at these energies. Moreover, it was shown that a resonance should appear below 2Llo, if the interaction between the produced two rotons is attractive. This resonance was clearly observed in the experiment by Murray, Woerner and Greytak. 5 )