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Journal Article

#### A Detailed Examination of Astrophysical Constraints on the Symmetry
Energy and the Neutron Skin of ^{208}Pb with Minimal Modeling Assumptions

##### External Resource

https://doi.org/10.1103/PhysRevC.104.065804

(Publisher version)

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##### Fulltext (public)

2107.05528.pdf

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##### Supplementary Material (public)

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##### Citation

Essick, R., Landry, P., Schwenk, A., & Tews, I. (2021). A Detailed Examination
of Astrophysical Constraints on the Symmetry Energy and the Neutron Skin of ^{208}Pb with Minimal Modeling Assumptions.* Physical Review C,* *104*(6): 065804. doi:10.1103/PhysRevC.104.065804.

Cite as: https://hdl.handle.net/21.11116/0000-0009-C34F-3

##### Abstract

The symmetry energy and its density dependence are pivotal for many nuclear

physics and astrophysics applications, as they determine properties ranging

from the neutron-skin thickness of nuclei to the crust thickness and the radius

of neutron stars. Recently, PREX-II reported a value of $0.283\pm0.071$ fm for

the neutron-skin thickness of $^{208}$Pb, $R_{\rm skin}^{^{208}\text{Pb}}$,

implying a symmetry-energy slope parameter $L$ of $106\pm37$ MeV, larger than

most ranges obtained from microscopic calculations and other nuclear

experiments. We use a nonparametric equation of state representation based on

Gaussian processes to constrain the symmetry energy $S_0$, $L$, and $R_{\rm

skin}^{^{208}\text{Pb}}$ directly from observations of neutron stars with

minimal modeling assumptions. The resulting astrophysical constraints from

heavy pulsar masses, LIGO/Virgo, and NICER favor smaller values of the neutron

skin and $L$, as well as negative symmetry incompressibilities. Combining

astrophysical data with chiral effective field theory ($\chi$EFT) and PREX-II

constraints yields $S_0 = 33.0^{+2.0}_{-1.8}$ MeV, $L=53^{+14}_{-15}$ MeV, and

$R_{\rm skin}^{^{208}\text{Pb}} = 0.17^{+0.04}_{-0.04}$ fm. We also examine the

consistency of several individual $\chi$EFT calculations with astrophysical

observations and terrestrial experiments. We find that there is only mild

tension between $\chi$EFT, astrophysical data, and PREX-II's

$R_\mathrm{skin}^{^{208}\mathrm{Pb}}$ measurement ($p$-value $= 12.3\%$) and

that there is excellent agreement between $\chi$EFT, astrophysical data, and

other nuclear experiments.

physics and astrophysics applications, as they determine properties ranging

from the neutron-skin thickness of nuclei to the crust thickness and the radius

of neutron stars. Recently, PREX-II reported a value of $0.283\pm0.071$ fm for

the neutron-skin thickness of $^{208}$Pb, $R_{\rm skin}^{^{208}\text{Pb}}$,

implying a symmetry-energy slope parameter $L$ of $106\pm37$ MeV, larger than

most ranges obtained from microscopic calculations and other nuclear

experiments. We use a nonparametric equation of state representation based on

Gaussian processes to constrain the symmetry energy $S_0$, $L$, and $R_{\rm

skin}^{^{208}\text{Pb}}$ directly from observations of neutron stars with

minimal modeling assumptions. The resulting astrophysical constraints from

heavy pulsar masses, LIGO/Virgo, and NICER favor smaller values of the neutron

skin and $L$, as well as negative symmetry incompressibilities. Combining

astrophysical data with chiral effective field theory ($\chi$EFT) and PREX-II

constraints yields $S_0 = 33.0^{+2.0}_{-1.8}$ MeV, $L=53^{+14}_{-15}$ MeV, and

$R_{\rm skin}^{^{208}\text{Pb}} = 0.17^{+0.04}_{-0.04}$ fm. We also examine the

consistency of several individual $\chi$EFT calculations with astrophysical

observations and terrestrial experiments. We find that there is only mild

tension between $\chi$EFT, astrophysical data, and PREX-II's

$R_\mathrm{skin}^{^{208}\mathrm{Pb}}$ measurement ($p$-value $= 12.3\%$) and

that there is excellent agreement between $\chi$EFT, astrophysical data, and

other nuclear experiments.