“Model Hamiltonian for one- and two-dimensional superfluids”

A model Hamiltonian describing bosons in one and two space dimensions interacting via a repulsive interparticle potential is shown to give rise to the phenomenon of superfluidity. The model has macroscopic occupation of infinitely many single-particle quantum states and the energy spectrum of the elementary excitations exhibits both phonon and roton features. Relations are found between the roton parameters, the speed of first sound and the condensate fraction where any two of them can be taken as independent variables. It is also shown that the type of condensate considered is not excluded by any rigorous proof.