Diquark-diquark correlations in the $^1S_0$ $\Lambda \Lambda$ potential

We derive a $\Lambda \Lambda$ potential from a chiral constituent quark model that has been successful in describing one, two and three nonstrange baryon systems. The resulting interaction at low energy is attractive at all distances due to the $\sigma$ exchange term. The attraction allows for a slightly bound state just below the $\Lambda \Lambda$ threshold. No short-range repulsive core is found. We extract the diquark-diquark contribution that turns out to be the most attractive and probable at small distances. At large distances the asymptotic behavior of the $\Lambda \Lambda$ interaction provides a prediction for the $\sigma \Lambda \Lambda$ coupling constant.