Pedro Sanson | Searcharxiv

arXiv2026

Signatures of quark matter from neutron star mass-radius curve

Signatures of the presence of quark matter inside neutron stars are obtained from the analysis of more than 250,000 mass-radius curves that describe nucleonic, hyperonic and hybrid stars, based on five different hadronic relativistic mean-field models and four different descriptions of quark matter. A radius maximum occurring above $1.7\,M_\odot$ strongly favors quark matter inside the star. A second criterion identifying the presence of quark matter is $X>-0.2$km, where X=[R(2.0)-R(1.6)]-[R(1.6)-R(1.4)] is obtained from the radius of stars with 2.0, 1.6 and 1.4 $M_\odot$. It is also shown that most of the hyperonic stars have a radius maximum that peaks around 1.5$M_\odot$ and compactness below 0.27 for the maximum-mass configuration, while for the nucleonic stars that have a radius maximum, this peaks below 1.3$M_\odot$ and the compactness of the maximum-mass configuration lies above 0.26.

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arXiv2026

Hyperonic equation of state for neutron stars: A systematic Bayesian comparison of density-dependent and non-linear relativistic mean-field models

A systematic Bayesian inference study of the equation of state (EOS) of dense matter with strangeness is presented, extending five relativistic mean-field (RMF) models with both constant and density-dependent couplings to include the full baryon octet. The hyperon-nucleon couplings in the scalar channel are varied within ranges informed by hypernuclear data, while vector isoscalar couplings are fixed by the SU(6) symmetry quark model. Observational constraints from NICER (PSR J0030, J0437, J0740) and GW170817, theoretical constraints from chiral effective field theory ($χ$EFT) and perturbative QCD (pQCD), and experimental constraints from nuclear saturation properties are imposed simultaneously. We find that the inclusion of hyperons systematically reduces the maximum neutron star mass by $0.05$-$0.10,M_\odot$ across all models while increasing the radius at $1.4,M_\odot$ by $0.5$-$0.8$ km. The speed of sound exhibits a characteristic softening at densities $2$-$3,ρ_{\rm sat}$ coinciding with hyperon onset. All hyperonic models remain consistent with the $2,M_\odot$ constraint. Models with a more flexible isovector channel span a larger proton fraction when only nucleons are included. However, the extra flexibility is visibly suppressed by hyperons, meaning that the average proton distribution is independent of model flexibility when hyperons are included. Less flexible models show comparable or slightly increased proton fractions due to EOS stiffening when hyperons are included. Only a residual number of hyperonic equations of state give rise to a mass-radius curve with a negative slope at low masses. A $1.8,M_\odot$ neutron star with a radius larger than or similar to the radius of a $1.2,M_\odot$ star would provide strong evidence that the star contains baryonic degrees of freedom beyond nucleons.

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