G. C. Strinati and P. Pieri 2005 Europhys. Lett. 71 359 doi:10.1209/epl/i2005-10097-y
G. C. Strinati and P. Pieri
Show affiliationsA well-known problem with the many-body approximations for interacting condensed bosons is the dichotomy between the "conserving" and "gapless" approximations, which either obey the conservations laws or satisfy the Hugenholtz-Pines condition for a gapless excitation spectrum, in the order. It is here shown that such a dichotomy does not exist for a system of composite bosons, which form as bound-fermion pairs in the strong-coupling limit of the fermionic attraction. By starting from the constituent fermions, for which conserving approximations can be constructed for any value of the mutual attraction according to the Baym-Kadanoff prescriptions, it is shown that these approximations also result into a gapless excitation spectrum for the boson-like propagators in the broken-symmetry phase.
03.75.Hh Static properties of condensates; thermodynamical, statistical and structural properties
Issue 3 (August 2005)
Received 10 February 2005, accepted for publication 5 June 2005, in final form 5 June 2005
Published 13 July 2005
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