Nuclear matter

About: Nuclear matter is a research topic. Over the lifetime, 10180 publications have been published within this topic receiving 248261 citations.

Neutron star equation of state from the quark level in the light of GW170817

Abstract: Matter state inside neutron stars is an exciting problem in astrophysics, nuclear physics and particle physics. The equation of state (EOS) of neutron stars plays a crucial role in the present multimessenger astronomy, especially after the event of GW170817. We propose a new neutron star EOS "QMF18" from the quark level, which describes well robust observational constraints from free-space nucleon, nuclear matter saturation, heavy pulsar measurements and the tidal deformability of the very recent GW170817 observation. For this purpose, we employ the quark-mean-field (QMF) model, allowing one to tune the density dependence of the symmetry energy and study effectively its correlations with the Love number and the tidal deformability. We provide tabulated data for the new EOS and compare it with other recent EOSs from various many-body frameworks.

Equation of state of superfluid neutron matter and the calculation of the 1S0 pairing gap.

Abstract: We present a quantum Monte Carlo study of the zero-temperature equation of state of neutron matter and the computation of the {sup 1}S{sub 0} pairing gap in the low-density regime with {rho}<0.04 fm{sup -3}. The system is described by a nonrelativistic nuclear Hamiltonian including both two- and three-nucleon interactions of the Argonne and Urbana type. This model interaction provides very accurate results in the calculation of the binding energy of light nuclei. A suppression of the gap with respect to the pure BCS theory is found, but sensibly weaker than in other works that attempt to include polarization effects in an approximate way.

Extracting nuclear symmetry energies at high densities from observations of neutron stars and gravitational waves

Abstract: By numerically inverting the Tolman-Oppenheimer-Volkov (TOV) equation using an explicitly isospin-dependent parametric Equation of State (EOS) of dense neutron-rich nucleonic matter, a restricted EOS parameter space is established using observational constraints on the radius, maximum mass, tidal deformability and causality condition of neutron stars (NSs). The constraining band obtained for the pressure as a function of energy (baryon) density is in good agreement with that extracted recently by the LIGO+Virgo Collaborations from their improved analyses of the NS tidal deformability in GW170817. Rather robust upper and lower boundaries on nuclear symmetry energies are extracted from the observational constraints up to about twice the saturation density $\rho_{0}$ of nuclear matter. More quantitatively, the symmetry energy at $2\rho_{0}$ is constrained to $ E_{\mathrm{sym}}(2\rho_{0})= 46.9\pm 10.1$ MeV excluding many existing theoretical predictions scattered between $ E_{\mathrm{sym}}(2\rho_{0}) =15$ and 100 MeV. Moreover, by studying variations of the causality surface where the speed of sound equals that of light at central densities of the most massive neutron stars within the restricted EOS parameter space, the absolutely maximum mass of neutron stars is found to be 2.40 $ \mathrm{M}_{\odot}$ approximately independent of the EOSs used. This limiting mass is consistent with findings of several recent analyses and numerical general relativity simulations about the maximum mass of the possible super-massive remanent produced in the immediate aftermath of GW170817. deformability

Pairing in low-density Fermi gases

Abstract: In the theory of fermionic matter, the expansion about the low-density limit has been invaluable for understanding the structure of the theory and the role of the interaction. At low densities, the interaction needs only be characterized by its scattering length to get expansions for the energy density, excitation spectrum, etc. @1#. However, to our knowledge the pairing singularity has never been incorporated into this framework. We have for example only the qualitative statement in Ref. @1# that the pairing singularity is logarithmic and unimportant for integrated quantities. A more quantitative statement is needed to have complete understanding of low-density fermionic matter. Another motivation for our study is the general reexamination of nuclear physics with effective field theory which is now taking place @2‐9#. In the effective field theory approach, the interaction is systematically expanded in a power series in momentum with the object of getting relationships between observables such that the details of the shortdistance interaction need not be parameterized. We shall show here that the BCS theory of pairing is amenable to this approach, and the low-energy theory gives finite and analytic results. Within effective field theory many results can be obtained analytically opposed to the numerical treatment of potential models. In this sense our approach complements the large body of literature of pairing in nuclear and neutron matter that is based on potential models @10‐16#. We consider a Fermi gas with two-fold degeneracy interacting with a short-range attractive interaction. Examples are neutron matter or gaseous 3 He. The Hamiltonian is idealized to be of the form