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QCD Baryons in the 1/Nc Expansion

E. Jenkins

hep-pharXiv:hep-ph/0111338

Abstract

The 1/Nc expansion provides a theoretical method for analyzing the spin-flavor symmetry properties of baryons in QCD that is quantitative, systematic and predictive. An exact spin-flavor symmetry exists for large-Nc baryons, whereas for QCD baryons, the spin-flavor symmetry is approximate and is broken by corrections proportional to the symmetry-breaking parameter 1/Nc = 1/3. The 1/Nc expansion predicts a hierarchy of spin and flavor symmetry relations for QCD baryons that is observed in nature. It provides a quantitative understanding of why some SU(3) flavor symmetry relations in the baryon sector, such as the Gell-Mann--Okubo mass formula, are satisfied to a greater precision than expected from flavor symmetry-breaking suppression factors alone.

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