Massive Meson Fluctuation in NJL Model**The project supported by National Natural Science Foundation of China (Nos 19677102 and 19845001)

Abstract

Based on the self-consistent scheme beyond the mean-field approximation in the large Nc expansion, including current quark mass explicitly, a general scheme of SU(2) NJL model is developed. To ensure the quark self-energy expanded in the proper order of Nc,an approximate internal meson propagator is deduced, which is in order of O(l/Nc). In our scheme, adopting the method of external momentum expansion, all the Feynman diagrams are calculated in a unified way by only expanding the quark propagator. Our numerical results show that, different &om the mean-field approximation in which the explicitly chiral symmetry breaking is invisible, the effect of finite pion mass can be seen clearly when beyond the meanfield approximation.