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Phys. Rev. Lett. 94, 080401 (2005) [4 pages]

Justification of c-Number Substitutions in Bosonic Hamiltonians

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Elliott H. Lieb and Robert Seiringer
Department of Physics, Jadwin Hall, Princeton University, P.O. Box 708, Princeton, New Jersey 08544, USA

Jakob Yngvason
Institut für Theoretische Physik, Universität Wien, Boltzmanngasse 5, A-1090 Vienna, Austria

Received 16 December 2004; published 2 March 2005

The validity of substituting a c-number z for the k=0 mode operator a0 is established rigorously in full generality, thereby verifying one aspect of Bogoliubov's 1947 theory. This substitution not only yields the correct value of thermodynamic quantities such as the pressure or ground state energy, but also the value of |z|2 that maximizes the partition function equals the true amount of condensation in the presence of a gauge-symmetry-breaking term. This point had previously been elusive.

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.94.080401
DOI:
10.1103/PhysRevLett.94.080401
PACS:
05.30.Jp, 03.75.Hh, 67.40.–w