VARIATIONAL APPROACH TO THE DILUTE BOSE-GAS

We study the weakly interacting Bose gas in both two and three dimensi ons using a variational approach. In particular we construct the therm odynamic potential of the gas to within ladder approximation and find by minimization an accurate mean-field description of the dilute Bose gas. Using spin-polarized atomic hydrogen as a specific example. we ob tain an improved description of the Bose-Einstein condensed phase in t hree dimensions, and a signature of a phase transition in two dimensio ns. The latter cannot be found by a straightforward application of per turbation theory around the ideal Bose gas.