How Neutron Star Radii Encode the Dense-Matter Equation of State and Hadron-Quark Transition
Abstract
We investigate how future high-precision neutron star (NS) radius measurements encode microscopic information about the dense-matter equation of state (EOS), focusing on a possible first-order hadron--quark phase transition and the resulting mass--radius topology. Within a Bayesian framework using meta-model EOSs with nine microscopic parameters, we analyze mock radius measurements R1.4=11.9±σR km with σR=0.9 and $0.1$ km for canonical NSs. We introduce inverse EOS--radius mappings by studying the conditional mean of each EOS parameter as a function of the model-predicted canonical radius R1.4. Their slope measures the sensitivity of an EOS parameter to the radius, while their curvature determines the leading precision dependence of its posterior mean through the Jensen expansion. The symmetry-energy parameters L (slope) and Ksym (curvature) are strongly encoded in R1.4 and their posterior means shift appreciably with improved radius precision, whereas the higher-order hadronic parameters show stronger topology dependence. Among the transition parameters, the transition density ρt is the most strongly encoded in R1.4, while the energy-density jump and quark-matter sound speed are more strongly associated with the topology of the full mass--radius sequence. Since the different topologies have strongly overlapping R1.4 distributions, even precise radius measurements cannot by themselves identify the topology or uniquely determine the high-density transition properties. These results provide a parameter-dependent hierarchy for assessing the scientific return of future high-precision radius measurements and complementary probes of high-density NS EOS.
Related
- Neutron Star Merger Universality Relations for a Quark--Hadron Crossover Equation of State
- General-purpose equations of state for hadron-quark matter: first application to accretion-induced phase transitions in neutron stars
- Evidence for a Continuous Hadron--Quark Transition in Cold Dense Matter
- Axion effects on hybrid stars: earlier hadron-quark phase transition and larger quark-matter cores
- Axion effects on hybrid stars: earlier hadron-quark phase transition and larger quark-matter cores
BibTeX
@misc{li2026neutron,
title = {{How Neutron Star Radii Encode the Dense-Matter Equation of State and Hadron-Quark Transition}},
author = {Bao-An Li and Xavier Grundler},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.12632},
eprint = {2608.12632},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.12632},
note = {CC0},
}
RIS
TY - UNPB
TI - How Neutron Star Radii Encode the Dense-Matter Equation of State and Hadron-Quark Transition
AU - Bao-An Li
AU - Xavier Grundler
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2608.12632
UR - https://arxiv.org/abs/2608.12632
AB - We investigate how future high-precision neutron star (NS) radius measurements encode microscopic information about the dense-matter equation of state (EOS), focusing on a possible first-order hadron--quark phase transition and the resulting mass--radius topology. Within a Bayesian framework using meta-model EOSs with nine microscopic parameters, we analyze mock radius measurements R_1.4=11.9±σ_R km with σ_R=0.9 and $0.1$ km for canonical NSs. We introduce inverse EOS--radius mappings by studying the conditional mean of each EOS parameter as a function of the model-predicted canonical radius R_1.4. Their slope measures the sensitivity of an EOS parameter to the radius, while their curvature determines the leading precision dependence of its posterior mean through the Jensen expansion. The symmetry-energy parameters L (slope) and K_sym (curvature) are strongly encoded in R_1.4 and their posterior means shift appreciably with improved radius precision, whereas the higher-order hadronic parameters show stronger topology dependence. Among the transition parameters, the transition density ρ_t is the most strongly encoded in R_1.4, while the energy-density jump and quark-matter sound speed are more strongly associated with the topology of the full mass--radius sequence. Since the different topologies have strongly overlapping R_1.4 distributions, even precise radius measurements cannot by themselves identify the topology or uniquely determine the high-density transition properties. These results provide a parameter-dependent hierarchy for assessing the scientific return of future high-precision radius measurements and complementary probes of high-density NS EOS.
ER -