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

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

2004-06-22

arxiv.org/abs/hep-ph/0406237v1

Phys.Lett. B597 (2004) 173-181

Physics

High Energy Physics

High Energy Physics - Phenomenology

15 pages, 2 figures

Scientific paper

10.1016/j.physletb.2004.07.003

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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