A Chirally Symmetric, Confining Quark Model

Abstract

Quark models have provided a. good deal of our theoretical understanding of hadron physics in the low energy region where an application of Quantum Chromodynamics (QCD) so far requires lattice approaches. The price to pay for using models is that the range of applicability is limited. The MIT bag model, for instance, incorporates confinement, but violates the fundamental chiral symmetry of QCD. The pion mass therefore is unrealistically large in the MIT bag model^l. The Na.mbu Jona-Lasinio model, on the other hand, is based on a chirally symmetric Lagra.ngia.n, but does not confine². This implies that the pion mass and the pion decay constant can be reproduced well in the NJL — model, the pion form factor in the time-like region, however, acquires an unphysical width which is due to the emission of quarks³.