NJL模型中的外动量展开(英文)

External Momentum Expansion in NJL Model

建立了包括流夸克质量的SU（2）NJL模型超出平均场近似的一般框架．在这个框架内，组份夸克传播子按外动量展开，所有的费曼图可统一地得到计算．数值结果表明：在平均场近似下，流夸克质量的效应几乎看不见，只有超出平均场近似，流夸克质量的效应才能体现出来，并且NJL模型的参数更为合理．

In the large Nc expansion beyond mean-field approximation, we develop a generals scheme of SU(2) NJL model including current quark mass explicitly. In our scheme, the conshttituent quark's propagator is expanded in pion's external momentum k, and all the Feynman diagrams are naturally expanded to k2 term in a unified way. Our numerical results show that in the mean field appproximations the effect of current quark mass is invisible, however, the effect of current quark mass can be seen explicitly beyond mean-field approximation for reasonable choices of the parameters in NJL model.