Baryon Mass Splittings in the 1/N_c Expansion

The $I=0,1,2,3$ mass splittings of the spin-$1/2$ octet and spin-$3/2$ decuplet baryons are analyzed in the $1/\N$ expansion combined with perturbative flavor breaking. We show there is considerable experimental evidence that the baryon masses satisfy the hierarchy predicted by this expansion. Since flavor symmetry-breaking suppression factors alone are not sufficient to describe the observed hierarchy, we conclude that there is firm evidence for the $1/\N$ expansion in the baryon masses. Our analysis differs from non-relativistic $SU(6)$.