Hypernuclei and the hyperon problem in neutron stars

The likely presence of Lambda baryons in dense hadronic matter tends to soften the equation of state to an extent that the observed heaviest neutron stars are difficult to explain. We analyze this "hyperon problem" with a phenomenological approach. First, we review what can be learned about the interaction of Lambda particle with dense matter from the observed hypernuclei and extend this phenomenological analysis to asymmetric matter. We add to this the current knowledge on nonstrange dense matter, including its uncertainties, to conclude that the interaction between Lambda's and dense matter has to become repulsive at densities below three times the nuclear saturation density.