Flavour symmetry breaking in quark vacuum condensates

Using a QCD estimate on the quark-vacuum condensate ratio (ss)0/(uu)0 the authors show, by deriving a sum rule, that the ratio of the meson wavefunction renormalization constants ZK12//Zpi 1/2 may deviate considerably from the SU(3) symmetric value of unity. This in turn raises the value of the pion-nucleon sigma -term from what is normally expected from the conventional GMOR scheme of chiral symmetry breaking.

Pion-nucleon σ-term : a QCD assessment

Positivity conditions on the spectral representation of the pseudoscalar densities are used to obtain bounds on the quark vacuum condensate ratio (ss)/(uu). These relate (ss)/(uu) to the topological susceptibility G(0) of the U(1) sector and appear to favour a smaller value for this quantity than is given by the current-algebra result.

S Debnath

Papers

Spectral function sum rules and the SU(3) violation of quark condensates in quantum chromodynamics