Vortex excitation in superfluid 4He: A Diffusion Monte Carlo study
  We present a diffusion Monte Carlo study of a single vortex in two-dimensional superfluid liquid $^4$He within the fixed node approximation. We use both the Feynman phase and an improved phase which includes backflow correlations to model the nodal surface of the vortex wavefunction. Results for the particle density, core radius and excitation energies are presented. 
S. Giorgini, J. Boronat and J. Casulleras (Universitat Politecnica de   Catalunya, Barcelona, Spain)