Medium effects in the Nambu-Iona-Lasinio model

Abstract

Several extensions and applications of the Nambu-Jona-Lasinio (NJL) model for an SU(2) symmetric theory are considered. First, we examine the effect of binding or confinement on the theory by means of a simple, naive, model. Second, we consider the particle-hole response function for scalar, pseudoscalar and vector excitations in the Bethe-Salpeter approximation. From the imaginary part of the response function we can deduce the masses of the corresponding mesons (σ, π, ω) and their coupling to the qq̄ excitations of the vacuum as well as to excitations of a quark medium.