New dispersive ΛNN force and s-shell hypernuclei

Variational Monte Carlo calculations for the ground- and excited-state binding energies of s-shell hypernuclei using a new form of dispersive spin-dependent noncentral ΛNN force have been made to study its effect on the overbinding problem of _Λ⁵He and on the spin dependence of ΛN force. A detailed analysis shows that the strength of the dispersive ΛNN force can be adjusted to resolve the overbinding problem using two-body correlations alone. Consequently, the ambiguity in the strength of the dispersive ΛNN force masks the effect of 2π-exchange ΛNN force and ΛNN correlations on the data. The contribution of the dispersive force to the 0⁺-1⁺ spin-flip splitting of A=4 hypernuclei is not uniquely determined. Further B_Λ data favor a small spin dependence of the ΛN potential, a situation characteristically similar to other versions of dispersive ΛNN potentials.