Possibility of a new neutral hypernucleus ⁴_ΛΛn = (n,n, Λ, Λ)

The status of the light hypernuclei is reviewed, and discussed with models based either on the Nijmegen-RIKEN baryon-baryon interaction or on recent studies using chiral effective field theory. The latter suggests a significantly shorter range for the ΛΛ interaction, and this favours the formation of a Borromean state made of two neutrons and two hyperons. Various corrections are discussed, in particular the coupling of NΛ to NΣ, or of ΛΛ to NΞ, and the role of tensor forces. The new nucleus ⁴_ΛΛn = (n,n, Λ, Λ) could be produced in various reactions, in particular deuteron-deuteron scattering with the simultaneous production of two charged kaons, for which an estimate of the cross section is provided