Search Results (4)

We discuss the neutron skins of ${}^{48}$Ca and ${}^{208}$Pb. We review and critically examine modern predictions and empirical constraints, with special attention to the different interpretations of the findings from the PREX-II experiment and the recently reported value of the neutron skin in ${}^{48}$Ca extracted from the CREX experiment. We argue that, in the spirit of the ab initio philosophy, the path to understanding the behavior of dense neutron-rich matter must not circumvent fundamental nuclear forces. Based only on that argument, a thick neutron skin in ${}^{208}$Pb is highly unlikely. Full article

A review is made of constraints on the nuclear symmetry energy parameters arising from nuclear binding energy measurements, theoretical chiral effective field predictions of neutron matter properties, the unitary gas conjecture, and measurements of neutron skin thicknesses and dipole polarizabilities. While most studies have been confined to the parameters $S_V$ and L, the important roles played by, and constraints on $K_{\mathrm{sym}}$, or, equivalently, the neutron matter incompressibility $K_N$, are discussed. Strong correlations among $S_V,L$, and $K_N$ are found from both nuclear binding energies and neutron matter theory. However, these correlations somewhat differ in the two cases, and those from neutron matter theory have smaller uncertainties. To 68% confidence, it is found from neutron matter theory that $S_V=32.0\pm 1.1$ MeV, $L=51.9\pm 7.9$ MeV and $K_N=152.2\pm 38.1$ MeV. Theoretical predictions for neutron skin thickness and dipole polarizability measurements of the neutron-rich nuclei ${}^{48}$Ca, ${}^{120}$Sn, and ${}^{208}$Pb are compared to recent experimental measurements, most notably the CREX and PREX neutron skin experiments from Jefferson Laboratory. By themselves, PREX I+II measurements of ${}^{208}$Pb and CREX measurement of ${}^{48}$Ca suggest $L=121\pm 47$ MeV and $L=-5\pm 40$ MeV, respectively, to 68% confidence. However, we show that nuclear interactions optimally satisfying both measurements imply $L=53\pm 13$ MeV, nearly the range suggested by either nuclear mass measurements or neutron matter theory, and is also consistent with nuclear dipole polarizability measurements. This small parameter range implies $R_{1.4}=11.6\pm 1.0$ km and ${\Lambda }_{1.4}={228}_{-90}^{+148}$, which are consistent with NICER X-ray and LIGO/Virgo gravitational wave observations of neutron stars. Full article

Recent experimental and ab initio theory investigations of the ${}^{208}$Pb neutron skin thickness have the potential to inform the neutron star equation of state. In particular, the strong correlation between the ${}^{208}$Pb neutron skin thickness and the pressure of neutron matter at normal nuclear densities leads to modified predictions for the radii, tidal deformabilities, and moments of inertia of typical $1.4M_{\odot }$ neutron stars. In the present work, we study the relative impact of these recent analyses of the ${}^{208}$Pb neutron skin thickness on bulk properties of neutron stars within a Bayesian statistical analysis. Two models for the equation of state prior are employed in order to highlight the role of the highly uncertain high-density equation of state. From our combined Bayesian analysis of nuclear theory, nuclear experiment, and observational constraints on the dense matter equation of state, we find at the 90% credibility level $R_{1.4}=12.{36}_{-0.73}^{+0.38}$ km for the radius of a $1.4M_{\odot }$ neutron star, $R_{2.0}=11.{96}_{-0.71}^{+0.94}$ km for the radius of a $2.0M_{\odot }$ neutron star, ${\mathsf{\Lambda }}_{1.4}={440}_{-144}^{+103}$ for the tidal deformability of a $1.4M_{\odot }$ neutron star, and $I_{1.338}=1.{425}_{-0.146}^{+0.074}\times {10}^{45}{\mathrm{g}\mathrm{cm}}^2$ for the moment of inertia of PSR J0737-3039A whose mass is $1.338M_{\odot }$. Full article

Background. We investigate possible correlations between neutron star observables and properties of atomic nuclei. In particular, we explore how the tidal deformability of a 1.4 solar mass neutron star, $M_{1.4}$, and the neutron-skin thickness of ${}^{48}$Ca and ${}^{208}$Pb are related to the stellar radius and the stiffness of the symmetry energy. Methods. We examine a large set of nuclear equations of state based on phenomenological models (Skyrme, NLWM, DDM) and ab initio theoretical methods (BBG, Dirac–Brueckner, Variational, Quantum Monte Carlo). Results: We find strong correlations between tidal deformability and NS radius, whereas a weaker correlation does exist with the stiffness of the symmetry energy. Regarding the neutron-skin thickness, weak correlations appear both with the stiffness of the symmetry energy, and the radius of a $M_{1.4}$. Our results show that whereas the considered EoS are compatible with the largest masses observed up to now, only five microscopic models and four Skyrme forces are simultaneously compatible with the present constraints on L and the PREX experimental data on the ${}^{208}$Pb neutron-skin thickness. We find that all the NLWM and DDM models and the majority of the Skyrme forces are excluded by these two experimental constraints, and that the analysis of the data collected by the NICER mission excludes most of the NLWM considered. Conclusion. The tidal deformability of a $M_{1.4}$ and the neutron-skin thickness of atomic nuclei show some degree of correlation with nuclear and astrophysical observables, which however depends on the ensemble of adopted EoS. Full article