Ground-state properties of a dilute two-dimensional Bose gas

We revisit the problem of the calculation of low-temperature properties for the dilute two-dimensional Bose gas. By using Popov's hydrodynamic approach and perturbation theory on the one-loop level we recover not only the known expansion for the ground-state energy but also calculate for the first time the condensate density and Tan's contact.
Comment: 10+epsilon pages, 1 figure; comments welcome