Europhys. Lett.
Volume 71, Number 3, August 2005
Page(s) 359 - 365
Section General
Published online 13 July 2005
Europhys. Lett., 71 (3), pp. 359-365 (2005)
DOI: 10.1209/epl/i2005-10097-y

Conserving and gapless approximations for the composite bosons in terms of the constituent fermions

G. 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