Flavour-symmetry breaking of the quark condensate and chiral corrections to the Gell-Mann–Oakes–Renner relation

The relation between the chiral quark condensate in QCD sum rules and chiral perturbation theory is clarified with the help of a low-energy theorem for the scalar and pseudoscalar correlation functions. It is found that the quark condensate should be identified with the non-normal-ordered vacuum expectation value of quark–antiquark fields. Utilising results on flavour SU(3) breaking of the quark condensate from QCD sum rules, the low-energy constant H2r in the chiral Lagrangian, as well as next-to-leading order corrections to the Gell-Mann–Oakes–Renner relation are estimated.