Multi-messenger and multi-physics Bayesian inference for GW170817 binary neutron star merger

Abstract

The tidal deformability probability distribution extracted from GW170817 alone, or including multi-messenger information, is confronted to astrophysical and nuclear physics additional constraints within a semi-agnostic approach for the dense matter equation of state. We use Bayesian statistics to combine together low density nuclear physics data, such as the ab-initio predictions based on χEFT interactions or the isoscalar giant monopole resonance, and astrophysical constraints from neutron stars, such as the maximum mass of neutron stars or the probability density function of the tidal deformability Λ obtained from the GW170817 event. The posteriors probability distribution functions are marginalized over several nuclear empirical parameters (Lsym, Ksym, Qsat and Qsym), as well as over observational quantities such as the 1.4M radius R1.4 and the pressure at twice the saturation density P (2nsat). The correlations between Lsym and Ksym and between Ksat and Qsat are also further analyzed. Tension is found between the posteriors: the first one is localized in the tidal deformability probability distribution itself, depending whether multi-messenger analysis is included or not, and the second one is between the observational data and the nuclear physics inputs. These tensions impact the predictions for Lsym, Ksym and R1.4 with centroids which differ by 2-3σ. Implications for the nuclear equation of state are also discussed.

Impact of the neutron-star deformability on equation of state parameters

“…After submission of this work for publication, we found that independently and in parallel, Ref. [44] conducts a very similar analysis using ELFc. Our work examines correlations between more parameters and our study extends to higher mass neutron star.…”

“…Ref. [44] uses much wider priors while our prior is more restrictive and provide finer details in a smaller phase-space. In addition, they apply additional constraints on the EOS using data from χEFT approach and ISGMR collective mode.…”

“…From the above considerations, we adopt ELFc in this study. Similar choice is also made in other recent studies [43,44]. The formulation of ELFc is detailed in Appendix B.…”

Neutron star tidal deformability and equation of state constraints

“…Finally, astronomical observations and terrestrial experiments can be translated to microscopic constraints through the symmetry energy [265], the energy budget for increasing asymmetry between neutrons and protons. Various studies have empirically identified correlations between various combinations of parameters that characterize the symmetry energy and its density dependence with the neutron star radius and tidal parameters [246,[266][267][268][269] or terrestrial experimental results [239,[270][271][272], as they all are linked to the low-density behavior of the equation of state around (twice) saturation. The tidal constraints from GW170817, and more recently radius constraints from NICER have been used to examine implications for the symmetry energy [273][274][275][276][277][278][279][280][281][282] as well as potential systematics in the mapping [283].…”

Unveiling the correlations of tidal deformability with the nuclear symmetry energy parameters

“…In the recent past, there have been several attempts to constrain the behavior of EoSs from the tidal deformability parameter using a diverse set of mean-field models [15,23,38,39], which satisfy some basic properties of finite nuclei. Similar studies are also carried out to constrain the EoS in a model independent manner [22,[40][41][42][43][44]. In particular, the method of construction of nuclear meta-models [45,46] based on the Taylor expansion around the saturation density ρ 0 has proved to be useful; the expansion coefficients are identified with the NMPs.…”