Isospin Breaking in the Nucleon Isovector Axial Charge from QCD Sum Rules
Jin, Xuemin
Original · EN
The isospin breaking in the nucleon isovector axial charge, gₐ³, are calculated within the external field QCD sum-rule approach. The isospin violations arising from the difference in up and down current quark masses and in up and down quark condensates are included; electromagnetic effects are not considered. We find δg³ₐ/g³ₐ ≈ (0.5-1.0)× 10⁻², where δg³ₐ = (g³ₐ)ₚ + (g³ₐ)ₙ and g³ₐ = [(g³ₐ)ₚ - (g³ₐ)ₙ]/2. Using the Goldberger-Treiman relation, we also obtain an estimate of the isospin breaking in the pion-nucleon coupling constant, (gppπ₀-gnnπ₀)/gNNπ ≈ (2-7) × 10⁻³.
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