${\mathrm{\Xi }}^{-}t$ quasibound state instead of $\mathrm{\Lambda }\mathrm{\Lambda }nn$ bound state

We study the coupled $\mathrm{\Lambda }\mathrm{\Lambda }nn-{\mathrm{\Xi }}^{-}pnn$ system to check whether the inclusion of channel coupling is able to bind the $\mathrm{\Lambda }\mathrm{\Lambda }nn$ system. We use a separable potential three-body model of the coupled $\mathrm{\Lambda }\mathrm{\Lambda }nn-{\mathrm{\Xi }}^{-}pnn$ system as well as a variational four-body calculation with realistic interactions. Our results exclude the possibility of a $\mathrm{\Lambda }\mathrm{\Lambda }nn$ bound state by a large margin. However, we have found a ${\mathrm{\Xi }}^{-}t$ quasibound state above the $\mathrm{\Lambda }\mathrm{\Lambda }nn$ threshold.