Phase transition and nuclear symmetry energy from neutron star observations: Constraints in light of PSR J0614--3329

Shao-Peng Tang; Yong-Jia Huang; Yi-Zhong Fan

doi:10.1103/bmsk-8n85

paper

Phase transition and nuclear symmetry energy from neutron star observations: Constraints in light of PSR J0614--3329

arXiv:2507.10025 · doi:10.1103/bmsk-8n85

Abstract

The possible occurrence of a first-order hadron-quark phase transition (FOPT) in neutron-star interiors remains an open question. Whether such a transition can be directly tested with improved observations is a key challenge. Here, we incorporate the latest constraints, especially a new NICER radius measurement for PSR J0614--3329, into a nonparametric Gaussian Process (GP) EOS framework that explicitly includes a first-order transition. We find a Bayes factor of $B \approx 2.3$ when comparing models with and without an explicit phase transition, marginally favoring its presence. At $68%$ credibility, the transition onset density $n_{PT}$ is either below $2 n_{s}$ (corresponding to masses $≲ 1 M_{⊙}$ , with density jump $Δ n \sim 0.5 n_{s}$ ) or, more prominently, above $4 n_{s}$ (near the central density of the heaviest NS, with $Δ n \sim 3 n_{s}$ ), where $n_{s}$ represents the nuclear saturation density. In addition, by using symmetry-energy expansion at low densities ( $< 1.1 n_{s}$ ), we infer a slope parameter $L = 40. 2_{- 14.3}^{+ 19.3}$ MeV, in good agreement with nuclear-experiment values. Intriguingly, $L$ correlates positively with the radius difference between $1.4 M_{⊙}$ and $2.0 M_{⊙}$ stars.

arXiv comment12 pages, 9 figures, PRD published

Phase transition and nuclear symmetry energy from neutron star observations: Constraints in light of PSR J0614--3329

Abstract

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