Approximating chiral SU(3) amplitudes

We construct large-Nc motivated approximate chiral SU(3) amplitudes of next-to-next-to-leading order. The amplitudes are independent of the renormalisation scale. Fitting lattice data with those amplitudes allows for the
extraction of chiral coupling constants with the correct scale dependence. The differences between approximate and full amplitudes are required to be at most of the order of N3LO contributions numerically. Applying the approximate expressions to recent lattice data for meson decay constants, we
determine several chiral couplings with good precision. In particular, we obtain a value for F0, the meson decay constant in the chiral SU(3) limit, that is more precise than all presently available determinations