Vacuum tunneling in superfluid helium-4 films

This work investigates vortex nucleation in two-dimensional superfluid helium-4 films via quantum tunneling, a phenomenon referred to as "Vortex Tunneling." Two primary mechanisms are explored under the ansatz that the effective mass of a vortex depends on its position within the film. The first mechanism is extrinsic vortex nucleation, where vortices nucleate from boundary surfaces; this is modeled by introducing a space-dependent correction to the vortex mass. The second mechanism is intrinsic vortex nucleation, a novel description of the tunneling of vortex-vortex pairs far from any boundary. This intrinsic model is further refined by incorporating dissipative corrections arising from the quasiparticle bath. These corrections are not introduced phenomenologically but are derived directly from the action of the theory, stemming from a QED-like coupling between the quasiparticle pair and the vortex core. This thesis provides a detailed calculation of the tunneling rates for both intrinsic and extrinsic processes, accounting for these new dynamic and dissipative effects.