Nuclear Matter In Neutron Stars Research Articles

Tidal Love numbers of neutron stars in Rastall gravity

Gravitational-wave measurements of the tidal deformability of neutron stars could reveal important information regarding their internal structure, the equation of state of high-dense nuclear matter and gravity in strong field regime. In this work, we extend the relativistic theory of the tidal deformability of neutron stars to Rastall gravity. Both the electric-type and magnetic-type quadrupole tidal Love numbers are calculated for neutron stars in the polytrope model. It is found that neutron star's tidal Love numbers in Rastall gravity is significantly smaller than those in general relativity. Our results provide new evidence of the degeneracy between the modification of gravity and the equation of state of nuclear matter in neutron stars.

Strongly Interacting Multi-component Fermions: From Ultracold Atomic Fermi Gas to Asymmetric Nuclear Matter in Neutron Stars

We investigate an asymmetric nuclear matter consisting of protons and neutrons with spin degrees of freedom (σ = ↑, ↓). By generalizing the Nozières and Schmitt-Rink theory for two-component Fermi gases to the four-component case, we analyze the critical temperature Tc of the superfluid phase transition. Although the pure neutron matter exhibits the dineutron condensation in the low-density region, the superfluid instability toward the deuteron condensation is found to take place as the proton fraction increases. We clarify the mechanism of the competition between the deuteron condensation and dineutron condensation. Our results would serve for understanding the properties of asymmetric nuclear matter realized in the interior of neutron stars.

Saturation of nuclear matter and roles of many-body forces: nuclear matter in neutron stars probed by nucleus—nucleus scattering

Yoichiro Nambu put a great foot print in nuclear physics in the era of its fundamental developments including his pioneering insight into essential ingredients of repulsive core of nuclear force and its relation to the saturation of nuclear matter. The present review article focuses onto recent developments of the interaction models between colliding nuclei in terms of Brueckner's G-matrix theory staring from realistic nuclear forces and the saturation property of symmetric nuclear matter as well as neutron-star matter. A recently proposed unique scenario of extracting the saturation property of nuclear matter and stiffness of neutron stars through the analysis of nucleus-nucleus elastic scattering in laboratories is presented in some detail.

A new study of the transition to uniform nuclear matter in neutron stars and supernovae

A comprehensive microscopic study of the properties of bulk matter at densities just below nuclear saturation $\rho_s = 2.5 \sim 10^{14}$ g cm$^{-3}$, zero and finite temperature and high neutron fraction, is outlined, and preliminary results presented. Such matter is expected to exist in the inner crust of neutron stars and during the core collapse of massive stars with $M \gtrsim 8M_{\odot}

Spectral Convexity for AttractiveSU(2N)Fermions

We prove a general theorem on spectral convexity with respect to particle number for 2N degenerate components of fermions. The number of spatial dimensions is arbitrary, and the system may be uniform or constrained by an external potential. We assume only that the interactions are governed by an SU(2N)-invariant two-body potential whose Fourier transform is negative definite. The convexity result implies that the ground state is in a 2N-particle clustering phase. We discuss implications for light nuclei as well as asymmetric nuclear matter in neutron stars.

Variational theory of hot nucleon matter

We develop a variational theory of hot nuclear matter in neutron stars and supernovae. It can also be used to study charged, hot nuclear matter which may be produced in heavy-ion collisions. This theory is a generalization of the variational theory of cold nuclear and neutron star matter based on realistic models of nuclear forces and pair correlation operators. The present approach uses microcanonical ensembles and the variational principle obeyed by the free energy. In this paper we show that the correlated states of the microcanonical ensemble at a given temperature $T$ and density \ensuremath{\rho} can be orthonormalized preserving their diagonal matrix elements of the Hamiltonian. This allows for the minimization of the free energy without corrections from the nonorthogonality of the correlated basis states, similar to that of the ground state energy. Samples of the microcanonical ensemble can be used to study the response, and the neutrino luminosities and opacities of hot matter. We present methods to orthonormalize the correlated states that contribute to the response of hot matter.

Bulk viscosity of magnetized neutron star matter

We study the effect of a magnetic field on the bulk viscosityof nuclear matter in neutron stars. We employ the framework ofrelativistic mean-field theory to model the dense nuclearmatter in neutron stars. The effects are first studied for thecase when the magnetic field does not exceed the criticalvalue to confine the electrons to the lowest Landau levels. Wethen consider the case ofan intense magnetic field to evaluate theviscosity for the URCA processes and show that the inequalitypF(e) + pF(p)⩾pF(n) is no longer required tobe satisfied for the URCA processes to proceed.

Elastodynamical properties of nuclear matter from the observed activity of neutron stars

The results of studies devoted to describing the large-scale motions of the nuclear matter of neutron stars are reviewed. The approach is based on the idea that stellar nuclear matter is an elastic Fermi continuum possessing the properties of a compensated magneto-active plasma. The fundamental dynamical equations of motion of self-gravitating nuclear matter are taken to be the equations of nuclear elastodynamics, formulated in the macroscopic theory of nuclear collective processes. A variational method is presented for calculating the frequencies of gravitational-elastic spheroidal ( s -mode) and torsional ( t -mode) vibrations of a neutron star, and the star’s stability with respect to linear deformations is studied. The effectiveness of the elastodynamical method is illustrated by calculations of the periods of global gravitational elastic vibrations within the standard homogeneous model, and also for a family of realistic models of neutron stars, constructed on the basis of the relativistic equation of gravitational equilibrium and the nuclear-matter equations of state taking into account the heterophase nature of the nuclear statistical equilibrium. The motions of the magnetized Ae phase of the neutron-star matter are described using the magneto-hydrodynamical approach, which is used to calculate the frequencies of toroidal and poloidal Alfven oscillations. It is emphasized that magneto-plasma vibrations can significantly affect the electromagnetic activity of pulsars.

Nuclear matter in relativistic mean field theory with isovector scalar meson

Relativistic mean field (RMF) theory of nuclear matter with the isovector scalar mean field corresponding to the δ-meson [ a 0(980)] is studied. While the δ-meson mean field vanishes in symmetric nuclear matter, it can influence properties of asymmetric nuclear matter in neutron stars. The RMF contribution due to δ-field to the nuclear symmetry energy is negative. To fit the empirical value, E s ≈ 30 MeV, a stronger ϱ-meson coupling is required than in the absence of the δ-field. The energy per particle of neutron matter is then larger at high densities than the one with no δ-field included. Also, the proton fraction of β-stable matter increases. Splitting of proton and neutron effective masses due to the δ-field can affect transport properties of neutron star matter.