Inverse-mapped density-dependent relativistic mean-field inference of the neutron-star equation of state with multi-messenger constraints

Abstract

We perform a Bayesian inference of the equation of state (EOS) of cold dense matter within a density-dependent relativistic mean-field (DD-RMF) model. An explicit inverse-mapping procedure reconstructs the density-dependent couplings from a physically interpretable ten-dimensional parameter set while enforcing thermodynamic consistency together with stability and causality conditions. The EOS is constrained by complementary multi-messenger data including chiral effective field theory calculations at low density, heavy-ion collision flow information at intermediate densities, NICER mass-radius posteriors, and the existence of approximately two-solar-mass pulsars. The combined constraints strongly restrict both isoscalar and isovector sectors. In particular, the chiral effective field theory band favors a relatively soft symmetry-energy slope around 38 MeV, corresponding to a compact canonical neutron-star radius of about 11.6 km. To reconcile the intermediate-density softness suggested by heavy-ion data with the high-density stiffness required by massive pulsars, the posterior prefers a moderately large Dirac effective mass at saturation together with correlated high-density limits of the scalar and vector couplings. The resulting sound-speed profile remains causal and shows significant stiffening above the conformal limit at several times nuclear saturation density, indicating strongly interacting matter in neutron-star cores. Evidence diagnostics indicate strong compatibility among the adopted constraints within the present DD-RMF framework.

Figures (11)

• Figure 1: Microphysical constraints employed in the likelihood function. (Left) The chiral effective field theory ($\chi$EFT) pressure band evaluated for pure neutron matter at sub-saturation densities taken from Ref. Keller2023PRL. (Right) The heavy-ion collision (HIC) pressure band constrained for symmetric nuclear matter at intermediate suprasaturation densities taken from Ref. Danielewicz2002_Science298-1592.
• Figure 2: One-dimensional marginalized posteriors for the 10 inferred parameters under different data selections. The shaded gray band shows the uniform priors. Colored curves show posteriors obtained with NS-only, $\chi$EFT-only, HIC-only, $\chi$EFT+HIC, $\chi$EFT+NS, HIC+NS, and the full ALL combination.
• Figure 3: Corner plot for the ALL dataset. Diagonal panels show 1D marginalized posteriors, while off-diagonal panels show 2D joint posteriors. Inner (outer) shaded regions correspond to 68% (90%) credible regions.
• Figure 4: Reconstructed coupling shape functions $f_i(n)=g_i(n)/g_i(n_0)$ inferred from individual datasets (top: $\chi$EFT-only; middle: HIC-only; bottom: NS-only). In each row, the gray band denotes the 90% prior interval and the colored band denotes the 90% posterior interval. The vertical dotted line marks saturation density ($n=n_0$).
• Figure 5: Reconstructed coupling shape functions inferred from the ALL dataset. The gray band shows the 90% prior interval and the blue band shows the 90% posterior interval. The multi-messenger combination yields narrow trajectories and exposes correlated isoscalar evolution together with a suppressed isovector channel at high density.