Chiral perturbation theory: Expansions in the mass of the strange quark

In a previous paper, we have shown how to systematically determine the low-energy structure of the Green functions in QCD. The present article extends this framework to expansions in the mass of the strange quark. We construct the generating functional of U(3)×U(3) which allows us to calculate the Green functions up to and including terms of order p⁴ (at fixed radio m_quark/p²) in terms of a few coupling constants which chiral symmetry leaves undetermined. We calculate the first non-leading term in the quark mass expansion of the order parameters , and of the masses and decay constants in the pseudoscalar octet. The three coupling constants which are not fixed by experimental low-energy information are estimated by invoking large-N_c arguments.