QCD isospin breaking ChPT low-energy constants from the instanton vacuum
arXiv:1002.0283 · doi:10.1103/PhysRevD.81.054029
Abstract
In the framework of the instanton vacuum model we evaluate the Chiral Perturbation Theory (ChPT) low-energy constants h_3,l_7. We found that in the instanton vacuum model the constant l_7 is very sensitive to the shape of the instanton and the instanton vacuum parameters. We evaluated the constant l_7 for two different zero-mode profiles and as a function of the average instanton size ρand inter-instanton distance R. Our result agrees with an old "order of magnitude" estimate of this constant from [1]. The obtained value of l_7 implies that the pure QCD contribution to the pion mass difference is small, ~1% of the observed experimental value.
17 pages, 4 Figures. In the version 2 several unclear statements were clarified