Physics – Condensed Matter – Quantum Gases
Scientific paper
2011-05-25
Phys.Rev.A83:053622,2011
Physics
Condensed Matter
Quantum Gases
16 pages, 7 figures
Scientific paper
10.1103/PhysRevA.83.053622
We rewrite the Lagrangian for a dilute Bose gas in terms of auxiliary fields related to the normal and anomalous condensate densities. We derive the loop expansion of the effective action in the composite-field propagators. The lowest-order auxiliary field (LOAF) theory is a conserving mean-field approximation consistent with the Goldstone theorem without some of the difficulties plaguing approximations such as the Hartree and Popov approximations. LOAF predicts a second-order phase transition. We give a set of Feynman rules for improving results to any order in the loop expansion in terms of composite-field propagators. We compare results of the LOAF approximation with those derived using the Popov approximation. LOAF allows us to explore the critical regime for all values of the coupling constant and we determine various parameters in the unitarity limit.
Chien Chih-Chun
Cooper Fred
Dawson John F.
Mihaila Bogdan
Timmermans Eddy
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