2D Bose condensation and Goldstone singularities

The present paper is dedicated to the investigation of a two-dimensional Bose system with the density-density type interparticle interaction. We showed the possibility of a finite temperature phase transition and investigated the Goldstone singularities for both homogeneous and vortex ground states. The critical exponents of the O(n>1) symmetric ϕ4 model were computed within the ε-expansion for ε=2.