QCD isospin breaking ChPT low-energy constants from the instanton vacuum
Abstract
In the framework of the instanton vacuum model we evaluate the Chiral Perturbation Theory (ChPT) low-energy constants h3,l7. We found that in the instanton vacuum model the constant l7 is very sensitive to the shape of the instanton and the instanton vacuum parameters. We evaluated the constant l7 for two different zero-mode profiles and as a function of the average instanton size and inter-instanton distance R. Our result agrees with an old "order of magnitude" estimate of this constant from [1]. The obtained value of l7 implies that the pure QCD contribution to the pion mass difference is small, ~1% of the observed experimental value.
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