1/Nc Countings in Baryons

Abstract

The $1/N_c$ power countings for baryon decays and configuration mixings are determined by means of a non-relativistic quark picture. Such countings are expected to be robust under changes in the quark masses, and therefore valid as these become light. It is shown that excited baryons have natural widths of $\mathcal{O}(N_c^0)$. These dominant widths are due to the decays that proceed directly to the ground state baryons, with cascade decays being suppressed to $\mathcal{O}(1/N_c)$. Configuration mixings, defined as mixings between states belonging to different $O(3)\times SU(2N_f)$ multiplets, are shown to be sub-leading in an expansion in $1/\sqrt{N_c}$ when they involve the ground state baryons, while the mixings between excited states can be $\mathcal{O}(N_c^0)$.

19 pages, 1 figure An omission that changes the conclusions on configuration mixings has been corrected

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