Mesonic Low-Energy Constants

We review the status of the coupling constants of chiral Lagrangians in the meson sector, the so-called low-energy constants (LECs). We emphasize the chiral SU(2) and SU(3) Lagrangians for the strong interactions of light mesons and discuss the theoretical and experimental input for determining the corresponding LECs. In the two-flavor sector, we review the knowledge of the LECs from both continuum fits and lattice QCD analyses. For chiral SU(3), next-to-next-to-leading-order (NNLO) effects play a much greater role. Our main new results are fits of the LECs Li at both next-to-leading order (NLO) and NNLO, making extensive use of the available knowledge of NNLO LECs. We compare our results with available lattice determinations. We then discuss resonance saturation of LECs and the convergence of chiral SU(3) to NNLO. Finally, we review the status of predictions for the LECs of chiral Lagrangians with dynamical photons and leptons.