  We introduce an effective scalar field theory to describe the He-IV phase
diagram, which can be considered as a generalization of the XY model which
gives the usual lambda-transition. This theory results from a Ginzburg-Landau
Hamiltonian with higher order derivatives, which allow to produce transitions
between the superfluid, normal liquid and solid phases of He-IV. Mean field and
Monte Carlo analyses suggest that this model is able to reproduce the main
qualitative features of He-IV phase transitions.
