Liquid-gas phase transition in strange hadronic matter with relativistic models

Abstract

International audienceBackground: The advent of new dedicated experimental programs on hyperon physics is rapidly boosting the field, and the possibility of synthetizing multiple strange hypernuclei requires the addition of the strangeness degree of freedom to the models dedicated to nuclear structure and nuclear matter studies at low energy. Purpose: We want to settle the influence of strangeness on the nuclear liquid-gas phase transition. Because of the large uncertainties concerning the hyperon sector, we do not aim at a quantitative estimation of the phase diagram but rather at a qualitative description of the phenomenology, as model independent as possible. Method: We analyze the phase diagram of low density matter composed of neutrons, protons and $\Lambda$ hyperons using a Relativistic Mean Field (RMF) model. We largely explore the parameter space to pin down generic features of the phase transition, and compare the results to ab-initio quantum Monte Carlo calculations. Results: We show that the liquid-gas phase transition is only slightly quenched by the addition of hyperons. Strangeness is seen to be an order parameter of the phase transition, meaning that dilute strange matter is expected to be unstable with respect to the formation of hyper-clusters. Conclusions: More quantitative results within the RMF model need improved functionals at low density, possibly fitted to ab-initio calculations of nuclear and $\Lambda$ matter

A Neutron Star Is Born

“…Parameter-dependent nuclear models can also explain the fusion of the elements in the stars and the primordial nucleosynthesis with the abundance of chemical elements in the observable universe, which is roughly the following: 71% is hydrogen, 27% is helium, 1.8% is carbon to neon elements, 0.2% is neon to titanium, 0.02% is lead and only 0.0001% is elements with atomic number larger than 60. By observing Figure 3, one easily identifies the element with the largest binding energy, 56 Fe. Hence, it is possible to explain why elements with atomic numbers A ≤ 56 are synthesised in the stars by nuclear fusion that are exothermic reactions, and heavier elements are expected to be synthesized in other astrophysical processes, such as supernova explosions and more recently also simulated in the mergers of compact objects.…”

“…Other examples of how to fit these couplings based on phenomenological potentials can be seen in [56,57]. The second possibility to choose the meson-hyperon couplings is based on the relations established among them by different group symmetries, the most common being SU(3) [52,58] and SU(6) [59].…”

$Δ$-admixed neutron stars: spinodal instabilities and dUrca processes

“…The curvature matrix analysis has been often employed in mean-field studies of baryonic matter. For the case of liquid-gas phase transition taking place at sub-saturation densities, see [44][45][46][47]; for strangeness-induced instabilities in dense strange hadronic matter, see [48][49][50][51][52].…”

Can generalized TOV equations explain neutron star macroscopic properties?

“…There are many approaches to fix the hyperon-meson couplings based either on the adjustments of pure phenomenological potentials [32,33] or on group symmetries [34]. In the present paper, we assume that [35]:…”