are not treated explicitly. Thus we employ the $\Lambda \Lambda$ interaction represented in the following three-range Gaussian form: $$v_{\Lambda \Lambda}(r)=\sum_{i=1}^{3}
   (v_i + v_i^\sigma
\mbox{\boldmath $\sigma$}_{\Lambda}\cdot
    \mbox{\boldmath $\sigma$}_{\Lambda})
               \: e^{-\mu_i r^2} .
%(3.6)$$

It is enlightening here to keep some linkage to the OBE models in determining the interaction parameters $\mu_i, v_i$ and $v_i^\sigma (i=1-3)$. In our previous work on $_\Lambda^{ }$$_\Lambda^6$He and $_\Lambda^{ }$$_\Lambda^{\!\!\!10}$Be [@Hiyama97], the interaction parameters were chosen so as to simulate the $\Lambda \Lambda$ sector of the ND interaction which is a reasonable model for the strong attraction suggested by the old interpretation for double-$\Lambda$ hypernuclei. The characteristic feature of ND is that there is only a scalar singlet instead of a scalar nonet, which gives strongly attractive contribution in $\Lambda \Lambda$ as well as $NN$.

The other versions of the Nijmegen models with a scalar nonet lead to much weaker $\Lambda \Lambda$ attractions, which seems to be appropriate for the weak $\Lambda \Lambda$ binding indicated by the NAGARA event. The NF is the simplest among these versions, which is adopted here as a guidance to construct our $\Lambda \Lambda$ interaction: The outer two components of the above Gaussian potential $(i=1,2)$ are determined so as to simulate 