Medium-mass hypernuclei and the nucleon-isospin dependence of the three-body hyperon-nucleon-nucleon force*

The appearance of hyperons in the core of a neutron star and the consequent softening of the equation of state have been questioned for a long time. The observation of massive neutron stars seems to rule out soft equations of state, apparently excluding the possibility of hyperon formation in the core of the star. The inconsistency between theoretical calculations and astrophysical observations, usually referred to as the hyperon puzzle, is based on our current knowledge of the interaction between strange particles and nucleons.

We give our contribution to the discussion by studying the general problem of the hyperon-nucleon interaction. We report quantum Monte Carlo calculations of single-Λ hypernuclei with A<50 based on phenomenological two- and three-body hyperon-nucleon forces. We present results for the Λ separation energy in different hyperon orbits, showing that the accuracy of numerical predictions exceeds that of currently available experimental data, especially for medium-mass hypernuclei. We show the results of a sensitivity study that indicates the possibility to investigate the nucleon-isospin dependence of the three-body hyperon-nucleon-nucleon force in the medium-mass region of the hypernuclear chart, where new spectroscopy studies are currently planned at the Thomas Jefferson National Accelerator Facility (JLab). The importance of such a dependence for the description of the physics of hypernuclei, and the consequences for the prediction of neutron star properties are discussed.