Meson loops in the Nambu-Jona-Lasinio model

Abstract The effects of meson loops in the vacuum sector of the Nambu-Jona-Lasinio model are calculated. Using the effective action formalism we take consistently all next-to-leading-order 1 N c terms into account. This leads to a symmetry-conserving approach, in which all features of spontaneously broken chiral symmetry, such as the Goldstone theorem, the Goldberger-Treiman and the Gell-Mann-Oakes-Renner relations are preserved. Contributions to 〈 q q〉 and F π are calculated, and are shown to be substantial, at the level of 30%, consistent with the 1 N c expansion. The leading non-analytic terms in the chiral expansion of 〈 q q〉 , F π and m π have the same form as the one-loop results of chiral perturbation theory.