Lowest negative parity baryons in the $1/N_c$ expansion

We review a recently proposed approach to study the lowest negative parity baryons within the $1/N_c$ expansion. The method is based on the derivation of the matrix elements of SU(2N$_f$) generators for mixed symmetric $[N_c-1,1]$ flavor-spin states. Presently it is applied to the N = 1 band and a comparison is made with a former method based on the decoupling of the system into a symmetric core of $N_c-1$ quarks and an excited one. We prove that the decoupling is not necessary and moreover, it misses some important physical consequences.

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