Extended quark models and QCD

por Dr. Alexandr Andrianov (Universitat de Barcelona)

jueves 7 may. 1998 12:00 → 13:00 Europe/Madrid

Sala Seminarios (Dpto. de Fisica Teorica (UVEG))

In the talk the low energy effective action of QCD below the chiral symmetry scale will be discussed, including operators of higher dimensions which can be built from quark fields and their derivatives, without or with additional chiral fields. The quark effective action prepared in the QCD perturbation theory without explicit separation of chiral fields shares the features of the Nambu-Jona-Lasinio models being symmetric under chiral rotations but possessing the strong coupling constants which induce the dynamical creation of constituent quark mass and pions. The corresponding effective meson lagrangian represents a generalization of the linear sigma-model. The effective action which takes manifestly into account the dynamical formation of nearly massless pions (chiral fields) represents another way to describe the meson physics at low and intermediate energies. It starts from the chiral quark model and leads to a hybrid between the latter one and the NJL like model. In both cases the crucial role plays the matching to QCD with the help of requirement of chiral symmetry restoration at energies above the CSB scale. Qualitatively, they bring a different CSB patterns: in the NJL approach the lightest scalar meson is a partner of the pion whereas in the Extended CQM the scalar meson becomes a partner of the heavy pion (pi-prime meson). Two approaches will be compared in the number of parameters derived from the meson phenomenology and in their predictivity.