Bayesian Constraints on the Neutron Star Equation of State with a Smooth Hadron-Quark Crossover

TL;DR

This paper uses Bayesian inference to constrain the neutron star equation of state by integrating hadronic, quark matter, and crossover models with observational data, revealing strong constraints on symmetry energy but weak constraints on high-density physics.

Contribution

It introduces a unified Bayesian framework that simultaneously infers hadronic, quark, and crossover parameters, unlike previous studies assuming sharp phase transitions.

Findings

Current data strongly constrain the density dependence of nuclear symmetry energy.

High-density hadronic and quark matter parameters remain weakly constrained.

The trace anomaly shows a universal behavior across the EOS ensemble.

Abstract

We perform a Bayesian inference of the dense-matter equation of state (EOS) within a unified framework that incorporates hadronic matter, quark matter, and a smooth hadron-to-quark crossover. The EOS is constrained using physical consistency conditions, gravitational wave data from GW170817, NICER mass versus radius measurements, and hypothetical future high-precision radius observations. In contrast to most previous studies that assume a sharp first-order phase transition or fix part of the EOS, we simultaneously infer hadronic, quark, and crossover parameters within a single statistical framework. We find that current observations strongly constrain the density dependence of the nuclear symmetry energy, particularly its slope and curvature. In contrast, the highest density hadronic parameters and quark-matter properties remain only weakly constrained. We further show that the trace anomaly exhibits a remarkably universal behavior across the accepted EOS ensemble and remains largely insensitive to current observational constraints. This indicates that the present data primarily probe the low to intermediate density EOS. At the same time, robust inference of quark matter and genuinely high-density physics will require next-generation precision radius measurements or complementary observables.