New dispersive Lambda NN force and s-shell hypernuclei

Variational Monte Carlo calculations for the ground- and excited-state bind ing energies of s-shell hypernuclei using a new form of dispersive spin-dep endent noncentral Lambda NN force have been made to study its effect on the overbinding problem of He-5(Lambda) and on the spin dependence of RN force . A detailed analysis shows that the strength of the dispersive Lambda NN f orce can be adjusted to resolve the overbinding problem using two-body corr elations alone. Consequently, the ambiguity in the strength of the dispersi ve Lambda NN force masks the effect of 2 pi-exchange Lambda NN force and La mbda NN correlations on the data. The contribution of the dispersive force to the 0(+)-1(+) spin-flip splitting of A=4 hypernuclei is not uniquely det ermined. Further Bn data favor a small spin dependence of the Lambda N pote ntial, a situation characteristically similar to other versions of dispersi ve Lambda NN potentials. [S0556-2813(99)05105-5].