In the large $N_c$ limit, all hyperon decays involving the same quark diagram $Q\to Q'$ are described by a single weak form factor $\eta_{ QQ'}(w)$. No assumption on the mass of $Q$ or $Q'$ is necessary, making our results applicable to both $b\to c$ and $c\to s$ transitions. This same form factor describes both $\Lambda_Q\to\Lambda_{ Q'}$ and $\Sigma^{ (*)}_Q\to\Sigma^{ (*)}_{ Q'}$ transitions. The (non-)commutativity between the heavy quark and the large $N_c$ limits is briefly discussed under the definite example of $\Lambda_b\to\Lambda_c$ decay.
Categories: hep-ph