Universal three-body repulsion suggested by neutron stars

Abstract

Because of a serious inconsistency between theory and observation for the mass of hyperon‐mixed neutron stars, it is suggested that some “extra repulsion” is needed in hypernuclear systems. A 3‐body force repulsion is tested for two cases, a 2π‐exchange via Δ‐excitation type (2πΔ) and a string‐junction model (SJM) for the quark structure of baryons. It is found that the 2πΔ model generates an increasing repulsion with increasing density but cannot produce the “extra repulsion” in hyperon‐mixed neutron stars because it does not work on a Λ due to the lack of ΛΛπ direct coupling. It is pointed out that the “extra repulsion” should act universally, i.e., independent of baryon species. The SJM 3‐body repulsion can satisfy the condition of universality because of the flavor‐independence and the {2πΔ+SJM} scheme is shown to be a promising candidate for the “extra repulsion”, maintaining consistency with the empirical saturation property of nuclear matter.