Abstract
A new fit is done to obtain numerical values for the order p 4 low-energy-constants L i r in Chiral Perturbation Theory. This includes both new data and new calculated observables. We take into account masses, decay constants, K ℓ 4 , ππ and πK scattering lengths and slopes and the slope of the pion scalar formfactor. We compare in detail where the changes w.r.t. the 10 years old “fit 10” come from. We discuss several scenarios for estimating the order p 6 constants C i r and search for possible values of them that provide a good convergence for the ChPT series. We present two such sets. One big change is that the fits do not have the expected behaviour in the limit of large N c as well as before.
Highlights
Since its very beginning Chiral Perturbation Theory (ChPT)[1, 2, 3], the effective field theory of QCD at low energies, has been successful in the description of several hadronic observables
There most of the next-to-leading order (NLO) couplings were inferred both from phenomenology and from considerations lead by large Nc estimates
It urged to carry on a program and perform next-to-next-to-leading order (NNLO) calculations [4]
Summary
Since its very beginning Chiral Perturbation Theory (ChPT)[1, 2, 3], the effective field theory of QCD at low energies, has been successful in the description of several hadronic observables. We let the Cir couplings to take random values, they are forced to keep the size 1/(16π2)2 For some of the NLO constants such ranges are very wide This method shows that it is possible to fit the NNLO expressions to the observables with Cir of the expected size and it allows to study well the strong correlations between the couplings. In the appendix we present a table where we quote our estimates for the NNLO couplings
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