The density-functional method is applied to excess electrons and positronium atoms in helium fluids. The self-trapping is investigated in a fully self-consistent fashion, and formulas are given for the particle energy and Ps pick-off annihilation rate in quasifree as well as localized states. The numerical results compare well with experimental data. However, the need for a more sophisticated treatment of threshold effects near the onset of bubble formation is indicated.Peer reviewe
