Hyperons analogous to the Λ(1405)

The low mass of the $Λ(1405)$ hyperon with $j^P = 1/2^-$, which is higher than the ground state $Λ(1116)$ mass by 290 MeV, is difficult to understand in quark models. We analyze the hyperon spectrum in the bound state approach of the Skyrme model that successfully describes both the $Λ(1116)$ and the $Λ(1405)$. This model predicts that several hyperon resonances of the same spin but with opposite parity form parity doublets that have a mass difference of around 300 MeV, which is indeed realized in the observed hyperon spectrum. Furthermore, the existence of the $Ξ(1620)$ and the $Ξ(1690)$ of $j^P=1/2^-$ is predicted by this model. Comments on the $Ω$ baryons and heavy quark baryons are made as well.

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