An exchange symmetry expansion for the 2-point correlation function of the nonlinear Schroedinger model

We define an exchange symmetry expansion for the 2-point function of the nonlinear Schroedinger model. Each term in the expansion can be represented by a diagram and we give a prescription for turning each diagram into the integral it represents using a bare propagator and the exact 2-body S-matrix phase shift. The lowest two terms in the expansion are computed in the thermodynamic limit. The lowest term, the zero-exchange term, is used as a dressed propagator to sum in closed form the next lowest term. A comparison is made with other expansions of the 2-point function. (orig.)