Sigma-nucleus potential in A=28

Results of analysis of Σ+p scattering events in J-PARC E40 experiment: differential cross sections and phase shifts of 3S1 and 1P1 states

We performed a novel Σ+p scattering experiment at the J-PARC Hadron Experimental Facility. Approximately 2400 Σ+p scattering events were identified by a kinematical consistency check for the recoil proton. The differential cross sections of the Σ+p elastic scattering were derived with better precision than in previous experiments. By exploiting high-quality differential cross section data and the simple representation of Σ+p interaction in the SU(3) flavor symmetry, we performed a phase-shift analysis on hyperon-nucleon scattering data for the first time. The absolute value of the phase shift of the 3S1 channel, where a large repulsive force was predicted due to the Pauli exclusive effect between quarks, was evaluated. These results indicate that the interaction of the 3S1 channel in the Σ+p channel is moderately repulsive, as the Nijmegen extended-soft-core models predicted.

Hyperons: the strange ingredients of the nuclear equation of state

We review the role and properties of hyperons in finite and infinite nuclear systems. In particular, we present different production mechanisms of hypernuclei, as well as several aspects of hypernuclear γ-ray spectroscopy, and the weak decay modes of hypernuclei. Then we discuss the construction of hyperon-nucleon and hyperon-hyperon interactions on the basis of the meson-exchange and chiral effective field theories. Recent developments based on the so-called V low k approach and lattice quantum chromodynamics will also be addressed. Finally, we go over some of the effects of hyperons on the properties of neutron and proto-neutron stars with an emphasis on the so-called 'hyperon puzzle', i.e. the problem of the strong softening of the equation of state, and the consequent reduction of the maximum mass, induced by the presence of hyperons, a problem which has become more intriguing and difficult to solve due the recent measurements of approximately 2M ⊙ millisecond pulsars. We discuss some of the solutions proposed to tackle this problem. We also re-examine the role of hyperons on the cooling properties of newly born neutron stars and on the development of the so-called r-mode instability.

Experimental review of hypernuclear physics: recent achievements and future perspectives

Since the shutdown of several old proton synchrotrons, which played a fundamental role in the second generation experiments in hypernuclear physics performed in Europe, USA and Japan, some new experimental setups aiming to achieve sub-MeV energy resolution have been operating for a long time. Over the last decade the hypernuclear physics community has been committed to carrying out several third generation experiments by exploiting the potential offered by new accelerators, such as a continuous electron beam machine and a ϕ-factory. Large data samples were collected on specific items thanks to dedicated facilities and experimental apparatuses. The attention was mainly focused on both high-resolution spectroscopy and the decay mode study of single Λ-hypernuclei. Nowadays this phase is over but, until recently, important and, to some extent, unexpected results were achieved. An updated review of selected experimental results is presented, as well as a survey of perspectives for future studies.

The influence of the enhanced vector meson sector on the properties of the matter of neutron stars

This paper gives an overview of the model of a neutron star with non-zero strangeness constructed within the framework of the nonlinear realization of the chiral SU(3)L x SU(3)R symmetry. The emphasis is put on the physical properties of the matter of a neutron star as well as on its internal structure. The obtained solution is particularly aimed at the problem of the construction of a theoretical model of a neutron star matter with hyperons that will give high value of the maximum mass.

Effects of hyperons in binary neutron star mergers

Numerical simulations for the merger of binary neutron stars are performed in full general relativity incorporating both nucleonic and hyperonic finite-temperature equations of state (EOS) and neutrino cooling. It is found that even for the hyperonic EOS, a hypermassive neutron star is first formed after the merger for the typical total mass ≈2.7M(⊙), and subsequently collapses to a black hole (BH). It is shown that hyperons play a substantial role in the postmerger dynamics, torus formation around the BH, and emission of gravitational waves (GWs). In particular, the existence of hyperons is imprinted in GWs. Therefore, GW observations will provide a potential opportunity to explore the composition of neutron star matter.