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arXiv · hep-ph/0406237

Flavour-singlet g_A and the QCD sum rule incorporating instanton effects

Tetsuo Nishikawa
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Abstract

We derive a QCD sum rule for the flavour-singlet axial coupling constant $g_A^{(0)}$ from a two point correlation function of flavour-singlet axial vector currents in a one-nucleon state. In evaluating the correlation function by an operator product expansion we take into account the terms up to dimension 6. This correlation function receives an additional two-loop diagram which comes from an (anti-)instanton. If we do not include it, $g_A^{(0)}$ is estimated to be 0.8. However, the additional diagram due to instantons contributes negatively and reduces $g_A^{(0)}$ towards the experimental value.

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Tetsuo Nishikawa. 2004-06-22. Flavour-singlet g_A and the QCD sum rule incorporating instanton effects. https://doi.org/10.1016/j.physletb.2004.07.003

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