Thoughts about the utility of perturbative QCD in the cores of neutron stars – contribution to a roundtable discussion on neutron stars and QCD

Kurkela, Aleksi

doi:10.1051/epjconf/202227407008

Cited by 4 publications

(1 citation statement)

References 44 publications

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“…It is interesting to verify that for Set 3 (ξ > 0.015) the speed of sound has a nonmonotonous behavior; it attains a maximum around 4ρ 0 and decreases for larger densities. In [36,77], the authors study the behavior of the speed of sound at high density, extrapolating the equation of state to high densities using a Gaussian process EOS description. They condition the EOS to astrophysical observations, or to both astrophysical observations and pQCD, and verify that the QCD conditioning gives rise to a decrease of the speed of sound above ∼3ρ 0 after a steep rise until this density.…”

Section: Discussionmentioning

confidence: 99%

Spanning the full range of neutron star properties within a microscopic description

et al. 2023

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The high-density behavior of nuclear matter is analyzed within a relativistic mean field description with nonlinear meson interactions. To assess the model parameters and their output, a Bayesian inference technique is used. The Bayesian setup is limited only by a few nuclear saturation properties, the neutron star maximum mass larger than 2M ⊙ , and the low-density pure neutron matter equation of state (EOS) produced by an accurate N 3 LO calculation in chiral effective field theory. Depending on the strength of the nonlinear scalar vector field contribution, we have found three distinct classes of EOSs, each one correlated to different star properties distributions. If the nonlinear vector field contribution is absent, the gravitational maximum mass and the sound velocity at high densities are the greatest. However, it also gives the smallest speed of sound at densities below three times saturation density. On the other hand, models with the strongest nonlinear vector field contribution predict the largest radii and tidal deformabilities for 1.4M ⊙ stars, together with the smallest mass for the onset of the nucleonic direct Urca processes and the smallest central baryonic densities for the maximum mass configuration. These models have the largest speed of sound below three times saturation density, but the smallest at high densities, in particular, above four times saturation density the speed of sound decreases approaching approximately ffiffiffiffiffiffi 0.4 p c at the center of the maximum mass star. On the contrary, a weak nonlinear vector contribution gives a monotonically increasing speed of sound. A 2.75M ⊙ neutron star (NS) maximum mass was obtained in the tail of the posterior with a weak nonlinear vector field interaction. This indicates that the secondary object in GW190814 could also be an NS. The possible onset of hyperons and the compatibility of the different sets of models with perturbative QCD (pQCD) are discussed. It is shown that pQCD favors models with a large contribution from the nonlinear vector field term or which include hyperons.

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Section: Discussionmentioning

confidence: 99%

Spanning the full range of neutron star properties within a microscopic description

et al. 2023

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Ridges in rotating neutron-star properties due to first order phase transitions

Moreno,

Llanes-Estrada,

Lope-Oter

2023

Annals of Physics

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Unified neutron star equations of state calibrated to nuclear properties

Malik,

Pais,

Providência

2024

A&A

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Recently, a dataset of several equations of state (EOSs) for purely nucleonic stellar matter based on a nonlinear relativistic mean-field model prescription and constrained to properties of nuclear matter, state-of-the-art chiral effective-field theory calculations for low-density neutron matter, and astrophysical data were proposed. In this work, 21 unified neutron star EOSs were chosen from that dataset in such a way that a large range of values of the slope of the symmetry energy at saturation is covered. Several quantities are calculated and discussed, such as the proton fraction and the direct Urca behavior, the density dependence of the speed of sound and the trace anomaly, the crust-core transition properties, the compatibility with astrophysical observations, and the neutron matter properties from chiral effective-field theory calculations and pQCD constraints. We construct unified EOSs where the outer crust is given by the BSk22 functional and the inner crust is calculated from a compressible liquid drop approximation. The core is purely nucleonic; made of protons, neutrons, electrons, and muons; under charge neutrality; and in beta -equilibrium conditions. The correlation of the slope of the symmetry energy at saturation with the crust-core transition density and proton fraction is analyzed, and equations that translate these relations are proposed. Moreover, the spectral representation for all the EOSs is given, which is a convenient representation to study quasi-periodic oscillations with realistic EOSs. We show that several of these EOSs have in the center of the most massive neutron star a speed of sound squared on the order of $ 0.5$. Most of the EOSs predict a maximum central density on the order of about six times the nuclear saturation density. Three of the EOSs satisfy all of the constraints imposed. The 21 unified EOSs are available in the zenodo platform.

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Thoughts about the utility of perturbative QCD in the cores of neutron stars – contribution to a roundtable discussion on neutron stars and QCD

Cited by 4 publications

References 44 publications

Spanning the full range of neutron star properties within a microscopic description

Spanning the full range of neutron star properties within a microscopic description

Ridges in rotating neutron-star properties due to first order phase transitions

Unified neutron star equations of state calibrated to nuclear properties

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