Implication of multimessenger observations on the relativistic mean-field equation of state of dense nuclear matter and skin thickness of nuclei

TL;DR

This work constrains the relativistic mean-field equation of state for dense nuclear matter by marrying ab initio \(\chi\text{EFT}\) inputs with multimessenger neutron-star observations (GW170817 and NICER). Using Bayesian inference over six saturation properties and their RMF couplings, the authors derive tight posteriors for the EoS and predict neutron-skin thicknesses for $^{48}$Ca and $^{208}$Pb, finding consistency with CREX for Ca but tension with PREX for Pb. The results favor a relatively soft high-density EoS, yielding a 1.4 $M_\odot$ radius around $12.5$–$12.9$ km and a maximum mass near $2.17\,M_\odot$, with the $\omega$-$\rho$ coupling $\Lambda_{\omega\rho}$ gaining importance under additional constraints. A notable outcome is the lack of a clear correlation between Pb skin thickness and the symmetry-energy slope $L$, and a tension between Pb skin predictions and PREX could signal model incompleteness or new physics in dense matter.

Abstract

The composition and properties of infinite nuclear matter under extreme conditions of temperature and pressure remain incompletely understood. In this work, we constrain the equation of state (EoS) of nuclear matter - constructed within the framework of the Relativistic Mean Field (RMF) model - by combining results from chiral effective field theory and multimessenger observations of neutron stars. Using the saturation properties of nuclear matter, we generate a wide ensemble of EoS, which are subsequently constrained within a Bayesian framework. The resulting posterior distributions provide tight bounds on both the saturation parameters and the coupling constants of the RMF model. Our results indicate that the GW170817 event and the latest NICER observation favor a relatively soft EoS, leading to lower crust-core transition densities and thinner neutron star crusts. The radius of a $1.4\,M_\odot$ neutron star is tightly constrained to $12.508_{-0.241}^{+0.257}$ km, while the maximum mass reaches $2.174_{-0.123}^{+0.174}\,M_\odot$. Furthermore, our analysis reveals that the $ω$-$ρ$ coupling, which governs the density dependence of the symmetry energy, becomes increasingly significant under successive astrophysical constraints. Finally, the predicted neutron skin thickness of $^{48}$Ca agrees well with the CREX measurement, whereas that of $^{208}$Pb remains in tension with PREX-II. In contrast to earlier studies, we do not observe a clear correlation between the neutron skin thickness of $^{208}$Pb and the symmetry energy slope parameter $L$.

Figures (10)

• Figure 1: Corner plot depicting the posterior distributions of the nuclear saturation parameters. The diagonal panels display the one-dimensional marginalized distributions for each parameter, while the off-diagonal panels show the 90% contours for the two-dimensional joint probability density functions. The colored contours and distributions represent successive constraints applied in the order indicated by the legend. On top of each diagonal panels we also show the 68% credible interval for each parameter in the order indicated by the legend.
• Figure 2: Same as Figure \ref{['fig:corner_saturation']} but now for coupling constants.
• Figure 3: (a) Pressure vs baryon number density of matter in $\beta-$equilibrium. The different colored pairs of curves denote the 90 % credible‐interval boundaries of the posterior samples as constraints are successively imposed in the order as shown in the legend.
• Figure 4: The left panel (a) shows the 90% mass-radius contours and the right panel (b) mass vs tidal deformability contours for neutron stars corresponding to the posterior samples.
• Figure 5: Same as Fig. 3 but for (a) Proton fraction vs Number density, and (b) Sound Speed squared vs number density.