Implicit correlations within phenomenological parametric models of the neutron star equation of state

Legred, Isaac; Chatziioannou, Katerina; Landry, Philippe

doi:10.1103/physrevd.105.043016

Cited by 38 publications

(37 citation statements)

References 81 publications

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“…The nonparametric model we use is deliberately constructed to emphasize flexibility in EoS morphology and impose few correlations between high and low densities besides those dictated by the physical requirements of causality and thermodynamic stability. The intra-density correlations introduced by different parametric and nonparametric EoS models will be investigated in quantitative detail in upcoming work [72].…”

Section: Discussionmentioning

confidence: 99%

“…1 of [84]. This nonparametric approach offers two further advantages over more traditional parametric models [85][86][87]: it avoids (i) systematic errors and (ii) strong (and perhaps opaque) intra-density correlations [72] that arise from restricting the EoS to a specific functional form with finite parameters which will inevitably not match the correct EoS or prior information about it.…”

Section: B Nonparametric Eos Modelmentioning

confidence: 99%

“…To determine the implications of J0740+6620's radius measurement for NS matter, we employ a nonparametric model for the NS EoS based on Gaussian processes (GPs), which offers us the flexibility of an analysis that (i) is not tightly linked to specific nuclear models, (ii) can account for phase transitions, including strong firstorder phase transitions that result in disconnected stable branches in the mass-radius relation, and (iii) is not subject to the systematic errors that arise with parametrized EoS families described by a finite set of parameters. Additionally, the nonparametric EoS model allows us to probe a wider range of intra-density correlations in the EoS than parametric models, something especially relevant for the current data set, which targets a wide range of NS densities [72].…”

Section: Introductionmentioning

confidence: 99%

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Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

Legred,

Chatziioannou,

Essick

et al. 2021

Preprint

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X-ray pulse profile modeling of PSR J0740+6620, the most massive known pulsar, by the NICER and XMM-Newton observatories recently led to a measurement of its radius. We investigate this measurement's implications for the neutron star equation of state, employing a nonparametric EoS model based on Gaussian processes and combining information from other X-ray, radio and gravitationalwave observations of neutron stars. Our analysis mildly disfavors equations of state that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of 6.4. For EoSs with multiple stable branches, the transition mass from the hadronic to the hybrid branch is constrained to lie outside (1, 2) M . We also find that the conformal sound-speed bound is violated inside neutron star cores, implying that core matter is strongly interacting. The squared sound speed reaches a maximum of 0.79 +0.21 −0.26 c 2 at 3.51 +2.30 −1.76 times nuclear saturation density at 90% credibility. Since all but the gravitational-wave observations prefer a relatively stiff EoS, PSR J0740+6620's central density is only 3.0 +1.6 −1.6 times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in β-equilibrium.

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Section: Discussionmentioning

confidence: 99%

Section: B Nonparametric Eos Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

Legred,

Chatziioannou,

Essick

et al. 2021

Preprint

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“…At the current state of investigations with a limited neutron star data base and correspondingly large uncertainties, it is still justified to use parametric functional forms as long as they are sufficiently general. In the future many more data are expected and a non-parametric description of the EoS in terms of a Gaussian Process [39,40,74,128] or neural network [129] will be useful.…”

Section: A General Priorsmentioning

confidence: 99%

Inference of the sound speed and related properties of neutron stars

Brandes¹,

Weise²,

Kaiser³

2022

Preprint

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Information on the phase structure of strongly interacting matter at high baryon densities can be gained from observations of neutron stars and their detailed analysis. In the present work Bayesian inference methods are used to set constraints on the speed of sound in the interior of neutron stars, based on recent multi-messenger data in combination with limiting conditions from nuclear physics at low densities. Two general parametric representations are introduced for the sound speed cs in order to examine the independence with respect to choices for the parametrisation of Priors. Credible regions for neutron star properties are analysed, in particular with reference to the quest for possible phase transitions in cold dense matter. The evaluation of Bayes factors implies extreme evidence for a violation of the conformal bound, c 2 s ≤ 1/3, inside neutron stars. Given the presently existing data base, it can be concluded that the occurrence of a first-order phase transition in the core of even a two-solar-mass neutron star is unlikely, while a continuous crossover cannot be ruled out. At the same time it is pointed out that the discovery of a superheavy neutron star with a mass M ∼ 2.3 − 2.4 M would strengthen evidence for a phase change in the deep interior of the star.

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“…Other methods for constructing phenomenological parametric EOSs exist, such as the spectral method (Lindblom & Indik 2014). Legred et al (2022) have shown that parametric EOSs can introduce correlations between the pressures at different densities that add artificial restrictions to the EOSs that can bias inference results, and show that nonparametric methods, such as the Gaussian process method (Landry & Essick 2019) do not suffer from this type of bias.…”

Section: Equations Of Statementioning

confidence: 99%

Universal Relations for the Increase in the Mass and Radius of a Rotating Neutron Star

Konstantinou

Morsink

2022

ApJ

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Rotation causes an increase in a neutron star’s mass and equatorial radius. The mass and radius depend sensitively on the unknown equation of state (EOS) of cold, dense matter. However, the increases in mass and radius due to rotation are almost independent of the EOS. The EOS independence leads to the idea of neutron star universality. In this paper, we compute sequences of rotating neutron stars with constant central density. We use a collection of randomly generated EOSs to construct simple correction factors to the mass and radius computed from the equations of hydrostatic equilibrium for nonrotating neutron stars. The correction factors depend only on the nonrotating star’s mass and radius and are almost independent of the EOS. This makes it computationally inexpensive to include observations of rotating neutron stars in EOS inference codes. We also construct a mapping from the measured mass and radius of a rotating neutron star to a corresponding nonrotating star. The mapping makes it possible to construct a zero-spin mass–radius curve if the masses and radii of many neutron stars with different spins are measured. We show that the changes in polar and equatorial radii are symmetric, in that the polar radius shrinks at the same rate in which the equatorial radius grows. This symmetry is related to the observation that the equatorial compactness (the ratio of mass to radius) is almost constant on one of the constant-density sequences.

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Implicit correlations within phenomenological parametric models of the neutron star equation of state

Cited by 38 publications

References 81 publications

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter

Inference of the sound speed and related properties of neutron stars

Universal Relations for the Increase in the Mass and Radius of a Rotating Neutron Star

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