On the ground state of the two-dimensional non-ideal bose gas

The theory of the ground state of the two-dimensional non-ideal Bose gas is presented. The conditions for the validity of the ladder and the Bogolubov approximations are derived. These conditions ensure the existence of a Bose condensate in the ground state of two-dimensional systems. These conditions are different from the corresponding conditions for the three-dimensional case. The connection between the effective interaction and the two-dimensional scattering amplitude at some characteristic energy κ2/2m (≠0) is obtained (f(κ = 0) = ∞ in the two-dimensional case).