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Neutral baryonic systems with strangeness

We review the status as regards the existence of three- and four-body bound states made of neutrons and $Λ$ hyperons. For interesting cases, the coupling to neutral baryonic systems made of charged particles of different strangeness has been addressed. There are strong arguments showing that the $Λnn$ system has no bound states. $ΛΛnn$ strong stable states are not favored by our current knowledge of the strangeness $-1$ and $-2$ baryon-baryon interactions. However, a possible $Ξ^- t$ quasibound state decaying to $ΛΛnn$ might exist in nature. Similarly, there is a broad agreement about the nonexistence of $ΛΛn$ bound states. However, the coupling to $ΞNN$ states opens the door to a resonance above the $ΛΛn$ threshold.