Conserving and gapless approximations for the composite bosons in terms of the constituent fermionsG. C. Strinati and P. Pieri
Dipartimento di Fisica, Università di Camerino - I-62032 Camerino, Italy
received 10 February 2005; accepted in final form 5 June 2005
published online 13 July 2005
A 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.Ss - Degenerate Fermi gases.
03.75.Hh - Static properties of condensates; thermodynamical, statistical and structural properties.
05.30.Jp - Boson systems.
© EDP Sciences 2005