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Register a new userAre nuclear matter properties correlated to neutron star observables ?
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Jin-Biao Wei
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We investigate properties of nuclear matter and examine possible correlations with neutron star observables for a set of microscopic nuclear equations of state derived within the Brueckner-Hartree-Fock formalism employing compatible three-body forces. We find good candidates for a realistic nuclear EOS up to high density and confirm strong correlations between neutron star radius, tidal deformability, and the pressure of betastable matter. No correlations are found with the saturation properties of nuclear matter.
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We explore the equation of state for nuclear matter in the quark-meson coupling model, including full Fock terms. The comparison with phenomenological constraints can be used to restrict the few additional parameters appearing in the Fock terms which are not present at Hartree level. Because the model is based upon the in-medium modification of the quark structure of the bound hadrons, it can be applied without additional parameters to include hyperons and to calculate the equation of state of dense matter in beta-equilibrium. This leads naturally to a study of the properties of neutron stars, including their maximum mass, their radii and density profiles.
A brief overview is given of the properties of spectral functions in finite nuclei as obtained from (e,ep) experiments. Based on recent experimental data from this reaction it is argued that the empirical value of the saturation density of nuclear matter is dominated by short-range correlations. This observation and the observed fragmentation and depletion of the single-particle strength in nuclei provide the motivation for attempting a self-consistent description of the nucleon spectral functions with full inclusion of short-range and tensor correlations in nuclear matter. Results for these ``second generation spectral functions will be discussed with emphasis on the consequences for the saturation properties of nuclear matter. Arguments are presented to clarify the obscuring role of pionic long-range correlations in this long-standing problem.
New observational data of neutron stars since GW170817 have helped improve our knowledge about nuclear symmetry energy especially at high densities. We have learned particularly: (1) The slope parameter $L$ of nuclear symmetry energy at saturation density $rho_0$ of nuclear matter from 24 new analyses is about $Lapprox 57.7pm 19$ MeV at 68% confidence level consistent with its fiducial value, (2) The curvature $K_{rm{sym}}$ from 16 new analyses is about $K_{rm{sym}}approx -107pm 88$ MeV, (3) The magnitude of nuclear symmetry energy at $2rho_0$, i.e. $E_{rm{sym}}(2rho_0)approx 51pm 13$ MeV at 68% confidence level, has been extracted from 9 new analyses of neutron star observables consistent with results from earlier analyses of heavy-ion reactions and the latest predictions of the state-of-the-art nuclear many-body theories, (4) while the available data from canonical neutron stars do not provide tight constraints on nuclear symmetry energy at densities above about $2rho_0$, the lower radius boundary $R_{2.01}=12.2$ km from NICERs very recent observation of PSR J0740+6620 of mass $2.08pm 0.07$ $M_{odot}$ and radius $R=12.2-16.3$ km at 68% confidence level sets a tight lower limit for nuclear symmetry energy at densities above $2rho_0$, (5) Bayesian inferences of nuclear symmetry energy using models encapsulating a first-order hadron-quark phase transition from observables of canonical neutron stars indicate that the phase transition shift appreciably both the $L$ and $K_{rm{sym}}$ to higher values but with larger uncertaintie , (6) The high-density behavior of nuclear symmetry energy affects significantly the minimum frequency necessary to rotationally support GW190814s secondary component of mass (2.50-2.67) $M_{odot}$ as the fastest and most massive pulsar discovered so far.
We have previously found a new phase of cold nuclear matter based on a holographic gauge theory, where baryons are introduced as instanton gas in the probe D8/$overline{rm D8}$ branes. In our model, we could obtain the equation of state (EOS) of our nuclear matter by introducing fermi momentum. Then, here we apply this model to the neutron star and study its mass and radius by solving the Tolman-Oppenheimer-Volkoff (TOV) equations in terms of the EOS given here. We give some comments for our holographic model from a viewpoint of the other field theoretical approaches.
The self-energy effect on the neutron-proton (np) pairing gap is investigated up to the third order within the framework of the extend Bruecker-Hartree-Fock (BHF) approach combined with the BCS theory. The self-energy up to the second-order contribution turns out to reduce strongly the effective energy gap, while the emph{renormalization} term enhances it significantly. In addition, the effect of the three-body force on the np pairing gap is shown to be negligible. To connect the present results with the np pairing in finite nuclei, an effective density-dependent zero-range pairing force is established with the parameters calibrated to the microscopically calculated energy gap.
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