Towards a determination of the chiral couplings at NLO in 1/N(C): L_8(mu) and C_38(mu)

摘要

We present a dispersive method which allows to investigate the low-energycouplings of chiral perturbation theory at the next-to-leading order (NLO) inthe 1/N(C) expansion, keeping full control of their renormalization scaledependence. Using the resonance chiral theory Lagrangian, we perform a NLOcalculation of the scalar and pseudoscalar two-point functions, within thesingle-resonance approximation. Imposing the correct QCD short-distanceconstraints, one determines their difference Pi(t)=Pi_S(t)-Pi_P(t) in terms ofthe pion decay constant and resonance masses. Its low momentum expansion fixesthen the low-energy chiral couplings L_8 and C_38. At mu_0=0.77 GeV, we obtainL_8(mu_0)^{SU(3)} = (0.6+-0.4)10^{-3} and C_{38}(mu_0)^{SU(3)}=(2+-6)10^{-6}.