Thermodynamic signatures do not uniquely identify deconfinement in neutron stars
Abstract
The smallness of polytropic index Γε ≲ 1.75 and near conformality of sound velocity cs2 ≈ 1/3 in neutron star matter are usually referred to as signals of the emergence of quark matter. We construct a density-resolved nucleonic reference domain in the (P/Pfree,Γε) plane using nucleonic EoSs jointly constrained by nuclear matter properties and neutron star mass, radius and tidal data, and found that the domain extends unambiguously below Γε=1.75. Crucially, the nucleonic domain becomes stable against the truncation order only after Z0 and Zsym are included, showing that the higher-order density dependence controls the extrapolation from finite nuclei to neutron-star matter. These findings therefore provide concrete targets for finite-nucleus and heavy-ion experiments, while linking terrestrial nuclear physics directly to multimessenger observations. We compare the domain with smooth equations of state generated by neural networks without phase labels and represented by symbolic regression. Among these reconstructions, 35.29% have complete trajectories inside the nucleonic domain over 0.5≤ n/n0≤8. Within the EoS sample obtained after minimizing the multimessenger loss, the smallest value of maxn cs2(n) is 0.38, above the conformal value 1/3. In conclusion, we convert microscopic interpretation into a falsifiable, density-resolved null-hypothesis test and show quantitatively that current observations do not reject the nucleonic null over much of the admissible space of equation of state.
Related
- Deconfinement Confined to the Heaviest Neutron Stars: Strange Quark Matter from a Flavor-Dressed Contact Interaction
- Thermodynamic signatures of the period-doubling route to chemical chaos
- Signatures in the local interstellar medium of electromagnetic radiation produced by neutron star gravitational waves
- Probing Nonlinear Logarithmic Kalb-Ramond Black Holes: Particle Dynamics, Epicyclic Oscillations and Thermodynamic Signatures
- Signatures of quark matter from neutron star mass-radius curve
BibTeX
@misc{ma2026thermodynamic,
title = {{Thermodynamic signatures do not uniquely identify deconfinement in neutron stars}},
author = {Yong-Liang Ma and Jia-Ying Xiong},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.01701},
eprint = {2610.01701},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.01701},
}
RIS
TY - UNPB
TI - Thermodynamic signatures do not uniquely identify deconfinement in neutron stars
AU - Yong-Liang Ma
AU - Jia-Ying Xiong
PY - 2026
DA - 2026/10/01
PB - arXiv
DO - 10.48550/arxiv.2610.01701
UR - https://arxiv.org/abs/2610.01701
AB - The smallness of polytropic index Γ_ε ≲ 1.75 and near conformality of sound velocity c_s^2 ≈ 1/3 in neutron star matter are usually referred to as signals of the emergence of quark matter. We construct a density-resolved nucleonic reference domain in the (P/P_free,Γ_ε) plane using nucleonic EoSs jointly constrained by nuclear matter properties and neutron star mass, radius and tidal data, and found that the domain extends unambiguously below Γ_ε=1.75. Crucially, the nucleonic domain becomes stable against the truncation order only after Z_0 and Z_sym are included, showing that the higher-order density dependence controls the extrapolation from finite nuclei to neutron-star matter. These findings therefore provide concrete targets for finite-nucleus and heavy-ion experiments, while linking terrestrial nuclear physics directly to multimessenger observations. We compare the domain with smooth equations of state generated by neural networks without phase labels and represented by symbolic regression. Among these reconstructions, 35.29% have complete trajectories inside the nucleonic domain over 0.5≤ n/n_0≤8. Within the EoS sample obtained after minimizing the multimessenger loss, the smallest value of max_n c_s^2(n) is 0.38, above the conformal value 1/3. In conclusion, we convert microscopic interpretation into a falsifiable, density-resolved null-hypothesis test and show quantitatively that current observations do not reject the nucleonic null over much of the admissible space of equation of state.
ER -