Interacting two-particle states in the symmetric phase of the chiral Nambu–Jona-Lasinio model

Abstract

The renormalization group flow of the chiral Nambu–Jona-Lasinio (NJL) model with one fermion flavor is mapped out in the symmetric phase with help of the Functional Renormalization Group (FRG) method using a physically motivated nonlocal trial effective action. The non-interacting infrared end-point of the flow of the four-fermion couplings is now accompanied by nonzero limiting composite couplings characteristic for interacting two-particle states with finite energy and physical size. The interaction energy of the constituents is extracted as a function of the physical size of the composite object. The propagation of a two-particle state minimizing the interaction energy has a natural bound state interpretation.