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Strangeness in nuclei and neutron stars: a challenging puzzle
The problem of determining a realistic interaction among hyperons and nucleons capable of reconciling the terrestrial measurements on hypernuclei and the recent observations of very massive neutron stars is still by and large unsolved. We attempt to give our contribution to the discussion by means of Auxiliary Field Diffusion Monte Carlo calculations for finite and infinite nuclear systems including strangeness. We employ a phenomenological approach showing that a refit of the three-body $\Lambda NN$ force on the available hyperon-separation energies provides the strong repulsive contribution needed to correctly describe the systematics of medium-light mass $\ Lambda$-hypernuclei.
The same potential has been used to determine the equation of state and the mass-radius relation of an infinite system containing neutrons and $\Lambda$ particles. Results show that the three-body hyperon-nucleon interaction plays a key role in the stiffness of the equation of state and on the predicted maximum mass. However, we stress the fact that more constraints on the hyperon-neutron forces are needed before drawing any conclusion on the role played by hyperons in neutron stars.