Flavor Symmetry Breaking in the 1/N Expansion

Abstract

The breaking of flavor SU(3) symmetry in the axial couplings and magnetic moments of baryons is analyzed in the $1/N_c$ expansion. A simple meson loop graph which is known to be of order $\sqrt{m_s}$ and leading order in $1/N_c$ correctly predicts the pattern of symmetry breaking in the magnetic moments. It is, however, not possible to use this graph to predict the magnitude of the breaking. The situation with the axial couplings is less clear. In this case the breakings are relatively small and do not appear to follow an obvious pattern. Nevertheless there is a clear indication that, with symmetry breaking taken into account, the F/D ratio (defined in the presence of SU(3) breaking) is considerably less than the SU(6) value of 2/3. With sizeable uncertainty, we find F/D \approx 0.44. The quantity 3F-D which is relevant for the analysis of spin-dependent deep inelastic scattering is considerably smaller than the SU(6) value of unity. The new value, 3F-D=0.27+-0.09, is consistent with vanishing strange-quark spin in the nucleon.

13 pages, 4 epsf figures, uses revtex

References in corpus (15)

• The 1/N Expansion for Baryons
• Measurement of the Spin-Dependent Structure Function $g_1(x)$ of the Proton
• Baryon-Pion Couplings from Large-N QCD
• Chiral Perturbation Theory Analysis of the Baryon Magnetic Moments
• Baryons from Quarks in the $1/N$ Expansion
• On Spin Independence in Large $N_c$ Baryons
• Baryon Hyperfine Mass Splittings in Large N QCD
• Baryon Mass Splittings in the 1/N_c Expansion
• Baryon Magnetic Moments in a Simultaneous Expansion in $1/N$ and $m_s$
• Light Quark Spin-Flavor Symmetry for Baryons Containing a Heavy Quark in Large N QCD
• Decays of $\ell =1$ Baryons --- Quark Model versus Large-$N_c$
• Baryon Magnetic Moments in the 1/N Expansion
• Hyperfine Mass Splittings of Baryons Containing a Heavy Quark in Large N QCD
• Spin Contents of Nucleons with SU(3) Breaking
• Reanalysis of hyperon beta decay data on $F/D$

Cited by in corpus (93)

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• First lattice QCD study of the gluonic structure of light nuclei
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• On the convergence of the chiral expansion for the baryon ground-state masses
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• The baryon vector current in the combined chiral and 1/Nc expansions
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• Baryon Magnetic Moments in Alternate 1/N_c Expansions
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• 1/N_c Expansion of the Heavy Baryon Isgur-Wise Functions
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• $1/m_Q$ and $1/N_c$ Expansions for Excited Heavy Baryons with Light Quarks in the Spin-Flavor Symmetric Representation
• Chiral corrections to the vector and axial couplings of quarks and baryons
• Lattice-QCD Determination of the Hyperon Axial Couplings in the Continuum Limit
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