Isospin Breaking and Instantons in QCD Nucleon Sum Rules

Abstract

We study isospin breaking instanton corrections to the operator product expansion of the nucleon correlation functions. After a comparison with quark model calculations based on the 't Hooft interaction, we examine the role of instantons in the corresponding QCD sum rules. Instanton contributions are found to be absent in the chirally even sum rule, but significant in the chirally-odd one. They improve the consistency of both sum rules and favor a value of the isovector quark condensate close to the chiral estimate.

28 pages, REVTEX file and 5 Postscript figures

References in corpus (8)

• Nucleon Properties from Unconventional Interpolating Fields
• Lattice Calculation of Point-to-Point Hadron Current Correlation
• Direct Instantons in QCD Nucleon Sum Rules
• The Electromagnetic Pion Form Factor and Instantons
• Baryon QCD sum rules in an external isovector-scalar field and baryon isospin mass splittings
• Calculation of $<p|\overline{u}u-\overline{d}d|p>$ from QCD sum rule and the neutron-proton mass difference
• Estimates of $m_d-m_u$ and $⟨\bar{d}d⟩-⟨\bar{u}u⟩$ from QCD sum rules for $D$ and $D^{\ast }$ isospin mass differences
• Electromagnetic Hadron Mass Differences and Estimation of Isotopic Symmetry Violation Parameters of QCD Vacuum from Quark Model

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• Analysis the $0^{++}$ nonet mesons as four-quark states with the QCD sum rules
• Direct Instantons and Nucleon Magnetic Moments
• Reanalysis the pentaquark ${\Theta }^{+}(1540)$ in the framework of QCD sum rules approach with direct instantons