Chiral effective lagrangian in the large-Nc limit: the nonet case Original Research Article

A UL (3) ⊗ UR(3) low-energy effective lagrangian for the nonet of pseudo-Goldstone bosons that appear in the large Nc limit of QCD is presented including terms up to four derivatives and explicit symmetry breaking terms up to quadratic in the quark masses. The one-loop renormalization of the couplings is worked out using the heat-kernel technique and dimensional renormalization. The calculation is carried through for UL(nl) ⊗ UR(nl), thus allowing for a generic number nl of light quark flavours. The crucial advantages that the expansion in powers of 1/Nc bring about are discussed. Special emphasis is put on pointing out what features are at variance with the SUL ⊗ SUR results when the singlet η′ is included in the theory.