Nuclear parameter inference with semi-agnostic priors

TL;DR

This paper investigates how neutron star observations can constrain nuclear matter properties using semi-agnostic priors, highlighting the importance of flexible equation-of-state models and analyzing the correlations between nuclear parameters and stellar observables.

Contribution

It introduces a semi-agnostic approach to infer nuclear empirical parameters from neutron star data, improving over fixed high-density assumptions.

Findings

Not all nuclear empirical parameters strongly correlate with pressure.

Semi-agnostic priors improve the recovery of nuclear parameters.

High-density parameterization can bias nuclear matter inference.

Abstract

Radio pulsar timing, X-ray pulse profile modeling or gravitational-wave detections of binary mergers involving at least one neutron star offer the opportunity to elucidate the properties of dense and neutron rich matter in thermodynamic regimes inaccessible to nuclear laboratories. Such inference relies on building appropriate equation-of-state priors, such as the recently introduced semi-agnostic constructions that incorporate nuclear theory and experimental information available in low to intermediate density regimes, while offering the necessary flexibility at high density. In this paper, we assess how detections of mass, radius, and tidal deformability for low-mass ($\sim 1$M$_{\odot}$) or high-mass ($\sim 1.9$M$_{\odot}$) neutron stars would contribute to constraining nuclear empirical parameters in an inference based on semi-agnostic equation-of-state priors. We first assessed the correlation factors between nuclear empirical parameters and the zero-temperature and $\beta$-equilibrated pressure in different regimes of density. We then simulate observations for three nucleonic equations of state to test the recovery of the corresponding nuclear empirical parameters. We show that not all nuclear empirical parameters significantly correlate with the pressure and find a competition between them in the high-density regime that challenges their inference. We also find that using semi-agnostic constructions instead of assuming a nucleonic content up to the highest densities in the neutron-star core can help recover more accurately the true nuclear empirical parameters. Parameterizing the high-density regime of the equation of state with the nucleonic meta-model can pollute the inference of nuclear empirical parameters; semi-agnostic constructions are a solution to that. However, many nuclear matter empirical parameters contribute in a similar way to the building of baryonic pressure.