Critical Point of a Weakly Interacting Two-Dimensional Bose Gas

We study the Berezinskii-Kosterlitz-Thouless transition in a weakly interacting 2D quantum Bose gas using the concept of universality and numerical simulations of the classical ||^4 model on a lattice. The critical density and chemical potential are given by relations n₂0ex{0ex}=0ex{0ex} (mT/2^2) ln (^2/mU) and ₂0ex{0ex}=0ex{0ex} (mTU/^2) ln (_^2/mU), where T is the temperature, m is the mass, and U is the effective interaction. The dimensionless constant 0ex{0ex}=0ex{0ex}3803 is very large and thus any quantitative analysis of the experimental data crucially depends on its value. For _ our result is _0ex{0ex}=0ex{0ex}13. 20. 4. We also report the study of the quasicondensate correlations at the critical point.