Vortex line in bulk 4 He

The core structure of a vortex in4He is still an open problem. Previous Monte Carlo variational computations have considered a vortex line in a small bucket so that the boundary conditions on the outer surface induce inhomogeneity in the system. We overcome this problem by considering 4 vortex lines of zero total vorticity in the simulation box and applying periodic boundary conditions. In this way we are essentially simulating an infinite array of vortices which is free of large scale flow. The first computation has been based on the Onsager-Feynman form of wave function. This gives an hollow core and the density dependence of the size of the core is studied. The case of a non-hollow core is under investigation. This is based on a shadow wave function for which the vorticity is distributed over a finite size.