Chiral Perturbation Theory for Mesons

Abstract

Chiral perturbation theory provides a systematic method for discussing the consequences of the global flavor symmetries of QCD at low energies by means of an effective field theory. The effective Lagrangian is expressed in terms of those hadronic degrees of freedom which, at low energies, appear as observable asymptotic states. At very low energies these are just the members of the pseudoscalar octet (π,K,η) which are regarded as the Goldstone bosons of the spontaneous breaking of the chiral SU(3)L×SU(3)R symmetry down to SU(3)V. The nonvanishing masses of the light pseudoscalars in the “real” world are related to the explicit symmetry breaking in QCD by the light-quark masses