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

Understand

The renormalisation group flow of the chiral Nambu--Jona-Lasinio (NJL) model with one fermion flavor is mapped out in the symmetric phase with the help of the Functional Renormalisation Group (FRG) method using a physically motivated non-local trial effective action.

• The well-known infrared unstable strongly coupled fixed point characterized by a set of pointlike four-fermion couplings is reproduced.
• The Gaussian infrared end-point of the flow of the four-fermion couplings is now accompanied by non-zero limiting composite couplings characteristic for interacting two-particle states with finite energy and physical size.
• The negative interaction energy of the constituents is extracted as a function of the physical size of the composite object.