  He-4 is known to become superfluid at very low temperatures. This effect is
now generally accepted to be connected with BEC (Bose-Einstein Condensation).
The dispersion relation of pressure waves in superfluid He-4 has been
determined at 1.1 {\deg}K by Yarnell et al., and exhibits a non monotonic
behavior - with a maximum and a minimum - usually explained in terms of
excitations called rotons, introduced by Landau. In the present work an attempt
is made to describe the phenomenon within the bohmian interpretation of QM. To
this end, the effects of the intermolecular potential, taken to be essentially
of the Lennard-Jones type modified to account for molecule finiteness, are
included as a Vlasov-type self-consistent field. A dispersion relation is
found, that is in quite good agreement with Yarnell's curve.
  Keywords: Bohm potential; Intermolecular potential; Dispersion relation;
Superfluid He-4; First sound.
  PACS: 05.30.Jp; 05.20.Dd; 03.75.Kk; 67.25.dt
