Accurate determination of the interaction between $\Lambda$ hyperons and nucleons from auxiliary field diffusion Monte Carlo calculations

An accurate assessment of the hyperon-nucleon interaction is of great interest in view of recent observations of very massive neutron stars. The challenge is to build a realistic interaction that can be used over a wide range of masses and in infinite matter starting from the available experimental data on the binding energy of light hypernuclei. To this end, accurate calculations of the hyperon binding energy in a hypernucleus are necessary. We present a quantum Monte Carlo study of $\Lambda$ and $\Lambda\Lambda$ hypernuclei up to $A=91$. We investigate the contribution of two- and three-body $\Lambda$-nucleon forces to the $\Lambda$ binding energy. Ground state energies are computed solving the Schr\"odinger equation for non-relativistic baryons by means of the auxiliary field diffusion Monte Carlo algorithm extended to the hypernuclear sector. We show that a simple adjustment of the parameters of the $\Lambda NN$ three-body force yields a very good agreement with available experimental data over a wide range of hypernuclear masses. In some cases no experiments have been performed yet, and we give new predictions. The newly fitted $\Lambda NN$ force properly describes the physics of medium-heavy $\Lambda$ hypernuclei, correctly reproducing the saturation property of the hyperon separation energy.